Apparatus and method for ammonia removal from waste streams

ABSTRACT

Apparatus, materials, and methods for removing ammonia from fluids using metal hydroxides (e.g. zinc hydroxide) and metal loaded media (e.g. zinc loaded ion exchange resins); the metal hydroxides and metal loaded media may be regenerated with a weak acid (pKa between 3 and 7). Alternatively, ammonia is removed from fluids by using H2SO4 and ZnSO4 and metal loaded media; the metal loaded media may be regenerated with H2SO4 and ZnSO4; the ammonia containing H2SO4 and ZnSO4 may be concentrated as necessary to form (NH4)2SO4.ZnSO4.6H2O (ammonium zinc sulfate hexahydrate) crystals. These crystals are removed from the mother liquor and heated to temperatures exceeding 200° C. releasing NH3 and H2O vapor upon the decomposition of the crystals.

This application is a continuation application and claims the benefit ofU.S. application Ser. No. 09/754,850 filed Jan. 4, 2001 which is nowabandoned; which is a continuation application and claims the benefit ofU.S. application Ser. No. 09/052,450 filed Mar. 31, 1998 which is nowabandoned; which application claims the benefit of U.S. ProvisionalApplication No. 60/042,175 filed Mar. 31, 1997, and U.S. ProvisionalApplication No. 60/060,079 filed Sep. 25, 1997.

The entire content of U.S. application Ser. No. 09/754,850 and Ser. No.09/052,450 including specification, claims, abstract, and drawings arehereby incorporated by reference as if fully rewritten herein.

FIELD OF THE INVENTION

The invention relates to methods, materials, and apparatus useful forreducing ammonia discharge from industrial and municipal waste streamsand for ammonia recovery. One aspect of the invention involves ammoniaabsorption using activated zinc hydroxide. Another aspect of theinvention involves ammonia absorption using sorbent for ligand exchangeadsorption with a metal bound to a cation exchange resin. A furtheraspect of the invention involves the regeneration and reuse ofabsorption media.

Another aspect of the invention involves the direct treatment of ammoniawaste streams with zinc sulfate and sulfuric acid and concentrating tocause crystallization of an ammonium zinc sulfate hydrate. Anotheraspect of the invention involves ammonia absorption using sorbent forligand exchange adsorption with a metal bound to a cation exchange resinand the subsequent regeneration using zinc sulfate and sulfuric acid toform the ammonium zinc sulfate hydrate crystals. In both aspects, thecrystals may then be heated to release NH₃ and regenerate the zincsulfate and sulfuric acid.

BACKGROUND OF THE INVENTION

Ammonia in aqueous solution is present as an equilibrium system definedby:NH₄ ⁺τNH₃+H⁺with an equilibrium constant of:$K_{a} = {\frac{\left\lbrack {NH}_{3} \right\rbrack\left\lbrack H^{+} \right\rbrack}{\left\lbrack {NH}_{4}^{+} \right\rbrack} = {5.848 \times 10^{- 10}}}$at 20° C. Where [NH₃] represents the concentration of dissolved neutralammonia. Techniques available for the removal of ammonia from aqueousstreams can normally only recover either the ionic [NH₄ ⁺] or gaseousform of ammonia [NH₃]. For efficient removal, adjusting the pH of theaqueous stream to a pH less than 7 or more than 11, maximizes theconcentration of either the ionic or gaseous form of ammoniarespectively. In actual practice, to maximize the concentration ofgaseous ammonia, the pH is typically adjusted to a value greater than 11using lime or sodium hydroxide.

The gaseous form of ammonia can be removed from water by air strippingwhere it is contacted with large volumes of air. As the volatility ofammonia increases with temperature, the current state-of-the art of airstripping occurs at higher temperatures. Many configurations ofcontacting equipment have been used, including countercurrent andcrosscurrent stripping towers, spray towers, diffused aeration, andstripping ponds with and without agitation. The ammonia has beenrecovered from the air by contacting the ammonia-laden air with sulfuricacid solution to form a solution of ammonium sulfate.

Steam stripping has also been used commercially, especially in theremoval of ammonia from sour waters. As with air stripping, steamstripping typically involves adjusting the pH to levels greater than 11using lime or sodium hydroxide. One process for treating petroleum sourwaters uses steam stripping which with further downstream processingresults in the recovery of ammonia in an anhydrous form, see Leonard etal., “Treating acid & sour gas: Waste water treating process”, ChemicalEngineering Progress, October, (1984), pp. 57-60. Mackenzie and King,“Combined solvent extraction and stripping for removal and isolation ofammonia from sour waters”, Industrial Eng. and Chem. Research, 24,(1985), pp. 1192-1200, have examined the combined use of steam strippingand solvent extraction for the removal of ammonia from sour waters withreduced steam consumption.

Cation exchange and zeolites have been used to recover the ammonium formof ammonia from aqueous streams, see for example Berry et al. “Removalof Ammonia From Wastewater”, U.S. Pat. No. 4,695,387 (1987), and Wirth,“Recovery of ammonia or amine from a cation exchange resin”, U.S. Pat.No. 4,263,145 (1981). For these uses the pH is typically adjusted tolower than neutral levels. Temperature plays a much less significantrole than in stripping. The cation exchange resins or zeolites are thenregenerated by treatment with metal hydroxide solutions to give gaseousammonia for which the resins and zeolites have no affinity.

References in the literature appear for the use of liquid membranes,hollow fibers, and reverse osmosis to remove ammonia from aqueousstreams, although none of these techniques have apparently beencommercialized.

Ligand exchange adsorption has been used to recover ammonia. In ligandexchange adsorption, an ion exchange resin is loaded with a complexingmetal ion such as Cu²⁺, Zn²⁺, Ni²⁺, Ag⁺, etc. (Helfferich, F., LigandExchange, I & II, Jnl. of the Am. Chem. Soc., No. 84, pp. 3237-3245,1962). The metal ion then acts as a solid sorbent for ligands such asammonia. In theory, each metal ion may adsorb a number of ligands up toits coordination number, normally 4 to 6. In practice, not all of thesesites will be occupied by an ammonia molecule.

When applied to ammonia, ligand exchangers will only form complexes withthe uncharged form of the ammonia. Dawson, in U.S. Pat. No. 3,842,000(1974) applied ligand exchange to the removal of ammonia from aqueousstreams. Dawson used Cu²⁺ as the metal ion because of its high aminecomplex formation constant and Dowex™ A-1 as the ion exchange resin.Ammonia was adsorbed after adjusting the pH of the solution to 9-12 toincrease the availability of dissolved gaseous ammonia. Contacting theligand exchange resin with a solution of sulfuric, nitric, phosphoric,or hydrochloric acid regenerated the ligand exchange resin. However,metal is stripped from the resin with each regeneration when a strongacid is used (see immediately below).

Dobbs et al. in “Ammonia removal from wastewater by ligand exchange”,Adsorption and Ion Exchange, AIChE Symposium Series, 71(152), (1975),pp. 157-163, examined the use of dilute hydrochloric acid and Jeffrey,M., Removal of ammonia from wastewater using ligand exchange, M. S.Thesis, Louisiana State University, (1977) (see Regeneration pp. 72-79),examined the use of dilute sulfuric acid as a regenerate for a Cu²⁺ligand exchange resin. Both dilute hydrochloric acid and dilute sulfuricacid were found to be ineffective as they leached the copper from theresin at unacceptably high levels. Both Jeffrey (1977) and Dobbs et al.(1975, 1976) attempted to use heat to remove the ammonia from the ligandexchange resin. Jeffrey's use of warm water up to 45° C. removed someammonia, but failed to prove an effective regeneration agent. Dobbs etal. (1975, and in U.S. Pat. No. 3,948,842) used 30 psig (21,000 kg/m²)steam as a regeneration agent. Although successful in regenerating mostof the ligand exchange resins activity, the process was energy intensiveand produced peak ammonia concentrations in the condensed steam of only800 ppm.

An object of the invention is to provide an ammonia recovery processthat is more economical than current methods for removal of ammonia fromfluid streams.

Another object of the invention is to provide an ammonia recoveryprocess that uses fewer chemicals than current processes or chemicalscompatible with the original process application. Typically thisinvolves regeneration and recycle of the sorbent material(s).

Another object of the invention is to reduce ammonia concentration inthe effluent stream to very low levels (i.e. less than or equal to 10ppm) or to control the ammonia concentration to meet environmentalregulations.

BRIEF DESCRIPTION OF THE INVENTION

Broadly the invention discloses methods and apparatus for the removal ofammonia from fluids, particularly industrial and municipal wastestreams. The waste streams may be gaseous or liquid streams.

I. First General Embodiment

A first embodiment of the invention includes a method for recoveringammonia from a fluid by the steps of: contacting the fluid with asorbent of metal loaded media; separating the sorbent containing ammoniafrom the fluid; separating the ammonia from the sorbent by contactingthe sorbent with a regenerant of a non-chelating weak acid, wherein anammonium regenerant salt is formed. In further embodiments there may beadditional steps including separating the ammonium from the ammoniumregenerant salt to form ammonia and free regenerant. The additionalsteps may include separating the ammonia from the ammonium regenerantsalt with a step selected from the group including: heating, applying avacuum and a combination thereof. More preferably the separation of theammonium from the regenerant salt is by the step of contacting with astrong acid to form regenerant and an ammonium strong acid salt; andseparating the regenerant therefrom. Typically the method includesrecycling the separated sorbent and/or recycling the separatedregenerant. Typically the weak acid may be a weak organic acid.Preferably the weak acid has a pK_(a) between about 3 and about 7. Themethod may be augmented by further treatment including contacting andreacting the separated ammonia with nitric acid to form ammoniumnitrate; and heating the ammonium nitrate and reacting at a temperatureand pressure under hydrothermal conditions to decompose the ammoniumnitrate to substantially nitrogen gas and water.

A more specific description of the first embodiment includes a methodfor recovering ammonia from a fluid including the steps of contactingthe fluid with a sorbent including a metal ion loaded media, in a manneradapted to sorb ammonia on the sorbent; separating the ammoniatedsorbent and the fluid; separating the ammonia from the sorbent bycontacting the ammoniated sorbent with a non-chelating weak acid to forman ammonium regenerant salt; separating the ammonia from the regenerantby one or more steps selected from the group including heating theammonium/regenerant complex; applying a vacuum to the ammonia/regenerantcomplex; or contacting the ammonia/regenerant complex with a strongacid.

Sorbent types useful in the invention typically include acrylamides,aminophosphonates, aminodiacetates, carboxylates, chelators,phosphonates, diphosphonates, and sulfonates.

A second further embodiment of the invention includes apparatus forrecovering ammonia from a fluid including: a container enclosing a metalloaded media, the metal loaded media able to reversibly sorb ammonia;one or more inlet valves at an inlet portion of the container foradmitting fluid or regenerant to the container; one or more outletvalves for exiting treated fluid or reacted regenerant at an outletportion of the container; and a source of regenerant that is anon-chelating weak acid, operatively connected to an inlet valve at theadmitting portion of the container. A further embodiment of theapparatus typically includes an ammonia separator for receiving andseparating ammonia from the regenerant, operatively connected to one ofthe outlet valves. A yet further embodiment includes a chemical reactoroperatively connected to the ammonia separator, for reacting separatedammonia from the separator with a strong acid; and a regenerantseparator, operatively connected to the reactor, for separating theregenerant from the strong acid. A yet further embodiment includesrecycling apparatus for providing regenerant from the regenerantseparator to the inlet valve. An additional embodiment includesapparatus for degrading the ammonia with a reactor for mixing andreacting nitric acid, operatively connected to the ammonia separator,for producing ammonium nitrate; and a hydrothermal reactor, operativelyconnected to the reactor, for degrading the ammonium nitrate tosubstantially gaseous nitrogen and water.

A yet further embodiment of the apparatus for recovering ammonia from afluid includes means for enclosing a metal loaded media able toreversibly sorb ammonia; inlet means, at an inlet portion of the meansfor enclosing, for admitting fluid or regenerant; outlet means, at anoutlet portion of the means for enclosing, for exiting treated fluid orreacted regenerant; and regenerant source means including anon-chelating weak acid, operatively connected to the inlet means.Additional embodiments can include means for separating ammonia from theregenerant, operatively connected to the outlet means.

Another embodiment for the apparatus includes reactor means forreceiving ammonia from the means for separating ammonia and reactingwith a strong acid and means for separating the regenerant from thestrong acid. Typically the apparatus includes means for recycling thesorbent and/or regenerant. Other embodiments typically include means forseparating ammonia from the reacted regenerant operatively connected tothe outlet means. Additional apparatus includes means for reactingnitric acid, operatively connected to the means for separating ammonia,to produce ammonium nitrate; and means for hydrothermally reacting theammonium nitrate, operatively connected to the means for reacting nitricacid, wherein the ammonium nitrate is reacted to essentially nitrogenand water.

Another embodiment of the invention includes methods for preparing metalloaded media including the steps of contacting the sorbent/resin with asolution of a soluble metal salt. The metal may be loaded at any pHwhere it is soluble. Loading is typically accomplished by increasing themetal ion concentration to the extent sufficient for outcompeting an H⁺ion at the sorbent/resin loading site

A second embodiment of the invention includes methods and apparatus forrecovery of ammonia from fluids based on a metal hydroxide sorbent.These methods typically include the steps of: contacting the fluid witha sorbent that is a solid metal hydroxide, so as to load ammonia on thesorbent; separating the sorbent loaded ammonia from the fluid;separating the ammonia from the sorbent by contacting the sorbent with aregenerant comprising a non-chelating weak acid, wherein an ammoniumregenerant salt is formed, at conditions where metal hydroxide is notsubstantially removed. Typically there are two methods that may be usedto assure that the metal hydroxide is not removed and is not availableas a sorbent. First, the weak non-chelating acid is added at a rate thatkeeps the pH above the dissolution point of the metal hydroxide.Secondly, the weak non-chelating acid is added at a rate where the metalhydroxide is not dissolved out of the system because the ultimateoverall pH of the system is still high enough to trap and reprecipitatethe metal hydroxide. The second method would be an advantage inovercoming surface fouling problems. In further embodiments there may beadditional steps including separating the ammonium from the ammoniumregenerant salt. The additional steps may include separating theammonium from the regenerant with a step selected from the groupincluding: heating, applying a vacuum, and/or contacting the salt with astrong acid to form regenerant and an ammonium strong acid salt; andseparating the regenerant therefrom. Typically the method includesrecycling the separated sorbent and/or recycling the separatedregenerant. In another embodiment the regenerant acid is typically aweak organic acid or a weak inorganic acid with a pK_(a) between about 3and about 7. The method may be augmented by further treatment includingcontacting and reacting the separated ammonia with nitric acid to formammonium nitrate; and heating the ammonium nitrate and reacting at atemperature and pressure under hydrothermal conditions to decompose theammonium nitrate to substantially nitrogen gas and water.

A yet further embodiment discloses methods for treating an air streamcontaining ammonia including contacting the air stream with a slurrymade up of particles of activated metal hydroxide, the particlesdispersed in a liquid; or particles of metal loaded media, the particlesdispersed in a liquid; and regenerating the particles and recovering theammonia. The particles are typically separated from the fluid streambefore prior to regenerating the particles. The particles having spentregenerant thereon may typically be regenerated with heat, a vacuum,with a weak acid, or a combination thereof. When activated metalhydroxide is selected, the additional step of regenerating the mediawith a weak acid must be made while maintaining the pH level above thatwhere metal is stripped from the metal hydroxide particle.

Generally this is accomplished by slow addition of weak acid and whilemaintaining the overall pH above 6 and most preferably above 7.

II. Second General Embodiment

A first embodiment of the invention includes a method for recoveringammonia from a fluid by the steps of contacting the fluid with a sorbentof metal-loaded media, separating the ammonia-containing sorbent fromthe fluid, separating the ammonia from the sorbent by contacting thesorbent with a stripping solution of a strong acid and a metal salt,wherein an ammonium salt is formed with the metal salt in a spentregeneration solution, separating the spent regeneration solution andtreating it to crystallize an ammonium-metal double salt therefrom.Typically, the crystallization is accomplished by increasing theconcentration of the ammonium salt and metal salt in the spentregeneration solution by evaporation or by decreasing the temperature ofhighly concentrated solutions. If desired crystallization may becontrolled by seeding.

Preferably the metal cation loaded on the metal-loaded media is den edfrom Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe (II and III), Hg, Mg, Mn, Ni,Pd, Zn, Zr. The metal cations may be used alone or in combination withone or more other metal cations. Preferably, the cation in the metalsalt of the stripping solution derives from Ag, Al, Ca, Ce, Cd, Co, Cr,Cu, Fe (II and III), Hg, Mg, Mn, Ni, Pd, Zn, Zr. The metal cations maybe used alone or in combination with one or more other metal cations.Preferably, at least some of the metal cations loaded on themetal-loaded media and the metal cations in the metal salt of thestripping solution are the same. More preferably, they are all the same.Zinc is preferred because of its nontoxic character in relation toanimals and humans and its solubility properties as a salt and doublesalt.

Preferably, the strong acid in the stripping solution is sulfuric,sulfurous, phosphoric and/or hydrochloric. More preferably, the strongacid is sulfuric. Typically, the anion in the metal salt used in thestripping solution matches the anion of the strong acid.

Preferably, concentration of the ammonium salt and metal salt in thespent regeneration solution is increased above the solubility limit ofthe ammonium-metal double salt with a step selected from the groupincluding: heating, applying a vacuum and a combination thereof. Morepreferably, these conditions will include seeding with recycled ammoniumsulfate crystals to minimize scaling and to control crystallization rateand crystal size.

In further embodiments there may be additional steps includingseparating the ammonia from the double salt and recycling the strippingsolution. The additional steps may include separating the ammonia fromthe ammonium-metal double salt by decomposition with heat.

Sorbent types useful in the invention typically include polymers ofacrylamides containing metal complex groups of aminophosphonates,aminodiacetates, carboxylates, phosphonates, diphosphonates, and/orsulfonates including chelators made therefrom and mixtures of theforegoing.

A more preferred embodiment includes contacting an ammonia-ladenwastewater stream with a zinc-loaded cation exchange resin to adsorb theammonia, separating the zinc-loaded cation exchange resin containing theadsorbed ammonia and stripping the ammonia with a stripping solution ofZnSO₄ and H₂SO₄ to form a spent regeneration solution of ammoniumsulfate and zinc sulfate, and crystallizing zinc ammonium sulfatehydrate therefrom. The method preferably includes recovering the zincammonium sulfate hydrate and decomposing to recover ammonia. Morepreferably, zinc sulfate and sulfuric acid are recovered from thedecomposition and recycled.

Crystallization of the zinc ammonium sulfate hydrate preferably includesevaporation of the spent regeneration solution in conventional mannerby, for example, heating, vacuum or a combination of the two, andsubsequent cooling. The amount of evaporation and cooling requireddepends upon the initial concentration of the ammonia. If the ammoniaconcentration is high enough (resulting in ammonium zinc sulfate hydrateconcentration above the solubility limit) no evaporation may berequired.

The crystals are preferably decomposed by heating wherein water andammonia vapors are released. Typically, the decomposition includesheating at a lower temperature to remove water, and subsequently heatingat a second higher temperature to remove ammonia. In certain situations,it may also be useful to drive the reaction further to release theSO₂/SO₃ and to then capture the gas as ammonium sulfate in conventionalways.

The ammonia may be captured as ammonia by condensation (particularly bymultiple effect condensation) or as a salt by using an acid stripper.The acid stripper (for example, phosphoric or nitric) can be selected toenhance the market value of the ammonia. After crystallization of thespent regeneration solution, the remaining aqueous liquid may be furtherprocessed to recover ammonium sulfate or it may be recycled backdirectly for ammonia stripping.

A second embodiment of the invention includes methods and apparatus fordirect reduction of ammonia from waste streams by reacting an aqueousammonia stream with a stripping solution of a strong acid and a metalsalt, wherein an ammonium salt is formed with the metal salt in a spentregeneration solution, separating the spent regeneration solution andtreating it to crystallize an ammonium-metal double salt therefrom.Typically, the crystallization is accomplished by increasing theconcentration of the ammonium salt and metal salt in the spentregeneration solution by evaporation or by decreasing the temperature ofhighly concentrated solutions.

Preferably, the cation in the metal salt of the stripping solutionderives from Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe (II and III), Hg, Mg,Mn, Ni, Pd, Zn, Zr. The metal cations may be used alone or incombination with one or more other metal cations. Zinc is preferredbecause of its nontoxic character in relation to animals and humans andits solubility properties as a salt and double salt.

Preferably, the strong acid in the stripping solution is sulfuric,sulfurous, phosphoric and/or hydrochloric. More preferably, the strongacid is sulfuric. Typically, the anion in the metal salt used in thestripping solution is substantially the same anion as in the strongacid.

Preferably, concentration of the ammonium salt and metal salt in thespent regeneration solution is increased above the solubility limit ofthe ammonium-metal double salt with a step selected from the groupincluding: heating, applying a vacuum and a combination thereof.Optionally, the process will include seeding with recycled ammoniumsulfate crystals to minimize scaling and to control crystallization rateand crystal size.

In further embodiments there may be additional steps includingseparating the ammonia from the double salt and recycling the strippingsolution substantially the same as described above for recovery ofammonia from the double salt in the first embodiment. The additionalsteps may include separating the ammonia from the ammonium-metal doublesalt by decomposition with heat.

A more preferred process for the direct reduction of ammonia from awaste stream includes reacting an aqueous ammonia stream with a zincsulfate and sulfuric acid solution to produce a spent regenerationsolution of zinc sulfate and ammonium sulfate and treating such solutionto cause crystallization of zinc ammonium sulfate hydrate. Preferably,the crystallization is caused by concentrating the stream by removingwater. Typically this is accomplished by evaporation by conventionalheating, vacuum or a combination of the two. The crystallization mayalso be caused by reducing the temperature of the zinc sulfate/ammoniumsulfate solution or by a combination of concentration and cooling.

The method may also include cooling the solution below thecrystallization temperature and continuously or sequentially separatingthe crystals of zinc ammonium sulfate hydrate. Multiple crystallizationsteps may be used. Optionally, the method may also include recoveringzinc from the liquid remaining from the crystallization step, preferablywith a cation exchange resin or using liquid-liquid extraction, forexample, and sulfuric acid regeneration, depending on the zincconcentration.

The method may also include the recovery of ammonia by decomposition ofthe zinc ammonium sulfate hydrate crystals to release NH₃ and H₂O, andmay further include recovery of the remaining zinc sulfate and sulfuricacid, which are recycled. The decomposition step may preferably compriseheating the crystals at a lower temperature to remove water, and raisingthe temperature to a higher level to remove ammonia. Ammonia vapor maypreferably be condensed to recover the ammonia or recovered as a salt bystripping with an acid.

The invention also includes apparatus for recovering ammonia from afluid including: a fluid-contacting device containing an ammonia sorbentof metal-loaded media, means for contacting the ammonia-containing fluidwith the ammonia sorbent and sorbing the ammonia thereon, means forremoving the ammonia-depleted fluid from the contacting device, meansfor contacting the ammonia-loaded sorbent with a stripping solution of astrong acid and a metal salt to form a spent regeneration solution ofammonium salt and metal salt, and means for treating the spentregeneration solution to crystallize an ammonium-metal double salttherefrom. Typically, the apparatus also may include an evaporator forincreasing the concentration of the ammonium salt and metal salt in thespent regeneration solution and/or a cooling device for cooling thespent regeneration to cause crystallization. The evaporator and thecooling device may be the same piece of apparatus.

The apparatus may also include one or more heating devices fordecomposing the crystals to release the water and ammonia vapors.Typically, the apparatus also includes a condenser to recover theammonia vapor or a contacting device to capture ammonia as a salt byusing an acid stripper.

A yet further embodiment discloses methods for treating an airstream-containing ammonia including contacting the air stream directlywith an aqueous stream of zinc sulfate and sulfuric acid or withparticles of metal-loaded media which are thereafter stripped of ammoniaby contact with a zinc sulfate/sulfuric acid solution; crystallizingammonium zinc sulfate hydrate from the solution, and decomposing thelatter to release the ammonia and regenerate the stripping solution.

The invention includes every novel feature and every novel combinationof features disclosed in the specification herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a zinc hydroxide recovery process only.

FIG. 2 is a schematic drawing of a reversible chemisorption apparatusand process for ammonia removal using ligand exchange adsorption withformic acid regeneration and partial formic acid recovery.

FIG. 3 is a schematic drawing of a combination of a zinchydroxide-ammonia recovery process and a NitRem process.

FIG. 4 is a fitting of a calculated Langmuir isotherm to measured datafor the adsorption of ammonia to zinc loaded Dowex™ 50WX2-400 resin inbatch experiments at pH=8.0, and at room temperature.

FIG. 5 is a fitting of a calculated Langmuir isotherm to measured datafor the sorption of ammonia to Zn(OH)₂ resin in batch experiments atpH=9.5, and at room temperature.

FIG. 6 is a calculated graph showing the amount of Zn(OH)₂ (precipitatedin the presence of ammonia) required to reduce the ammonia concentrationfrom 360 to 10 ppm in a single stage contactor. Calculated using theexperimentally obtained sorption isotherm and a literature value of theammonia dissociation constant.

FIG. 7 is a calculated graph showing the amount of Zn-Dowex™ 50WX2-400ion exchange resin required to reduce the ammonia concentration from 360to 10 ppm in a single stage contactor. Calculated using theexperimentally obtained sorption isotherm and a literature value of theammonia dissociation constant.

FIG. 8 is a graph showing ammonia breakthrough curves for pH 8.0, 100ppm total ammonia, on 6 ml of Zn-Dowex™ Ligand 50WX2-400 ion exchangeresin for four adsorption cycles.

FIG. 9 is a graph showing the regeneration of an exchange column packedwith Zn-Dowex™ Ligand 50WX2-400 ion exchange resin using acetic acid forthree desorption cycles.

FIG. 10 is a graph showing ammonia breakthrough curves for pH 8.0, 100ppm total ammonia, on 6 ml Zn-Dowex™ Ligand exchange resin for threedesorption cycles.

FIG. 11 is a graph showing the regeneration of an exchange column packedwith Zn-Dowex Ligand 50WX2-400 ion exchange resin using 20% formic acidfor three desorption cycles.

FIG. 12 is a schematic drawing of apparatus for ammonia removal usingligand exchange adsorption with steam regeneration.

FIG. 13 is a schematic drawing of apparatus for ammonia removal usingligand exchange adsorption with formic acid regeneration.

FIG. 14 is a schematic drawing of apparatus and process for ammoniarecovery by direct treatment of ammonia waste streams with sulfuric acidand excess zinc sulfate to form ammonium zinc sulfate hydrate andsubsequent decomposition by heating.

FIG. 15 is a schematic drawing of apparatus and process for ammoniarecovery by direct treatment of highly concentrated ammonia wastestreams with zinc sulfate and sulfuric acid to form ammonium zincsulfate hydrate and subsequent decomposition by heating.

FIG. 16 is a schematic drawing of apparatus and process for ammoniarecovery from waste streams by use of ammonium zinc sulfate hydratecrystallization and decomposition in the regeneration of zinc-loaded ionexchange resin where ammonia is in excess.

FIG. 17 is a schematic drawing of apparatus and process for ammoniarecovery from waste streams by use of ammonium zinc sulfate hydratecrystallization and decomposition in the regeneration of zinc-loaded ionexchange resin where zinc is in excess.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

I. First General Embodiment

Broadly the invention includes methods, materials, and apparatus forremoving ammonia from fluid streams. The fluid streams include gaseousand liquid streams. When gaseous streams are used the ammonia from thegaseous stream is first extracted into a liquid stream and thenextracted from the liquid stream.

Two main embodiments for ammonia recovery are disclosed herein. Thefirst uses zinc hydroxide for contacting a fluid stream and the seconduses a metal loaded ion exchange medium for contacting the fluid stream.Both embodiments are able to reversibly bind ammonia so that overallcosts for the methods are reduced. For example, a zinc hydroxide slurrycan absorb ammonia from a fluid stream. The zinc hydroxide ammoniareaction can be reversed at higher temperatures or under vacuum toproduce a wet ammonia gas stream, or with contact with a weak acid; ametal loaded ion exchange medium can also be used for ammonia recoverywith reversal of the reaction by the use of a weak acid. Definitions forvarious terms used herein are provided below.

Definitions

As used herein the following terms have meanings as follows:

-   -   Activated metal hydroxide—a metal hydroxide treated by        contacting with ammonia or other activating agent or during the        production of the metal hydroxide where the metal hydroxide has        increased ammonia absorption capacity compared to the untreated        metal hydroxide.    -   Weak acid—as used herein refers to an acid having a pK_(a)        between about 3 to about 7.5 and preferably between 3 to 6, that        is nonchelating with respect to the metal ions to be regenerated        in the exchange medium. Typical weak acids useful in the        invention include weak organic acids such as acetic acid, formic        acid and the like, and weak inorganic acids such as nitrous acid        and the like (see Table 6). The pK_(a) ranges are important;        because, it has been found that metal is stripped from the ionic        exchange resins by use of regenerant acids having a low pK_(a)        such as below about 3 and very definitely below 2 and below 1.    -   Sorbent—as used herein includes polymeric materials and solid        materials having a surface area able to bind ammonia. The term        sorbent and its related terms of speech are used generally        herein to include both chemical and physical absorbents and        adsorbents.    -   Metal loaded media—as used herein includes metal loaded ion        exchange materials, chelating materials, zeolites, and organic        or inorganic materials. The important characteristic for these        metal loaded media is that they be capable of reversibly binding        ammonia. The metal should be firmly bound to the substrate        material so as not to substantially unbind during the conditions        of use. The metal loaded media should bind ammonia on exposure        to an ammonia containing fluid stream and give up the ammonia        when exposed to a weak acid.

Pretreatment of the waste streams used in the invention is contemplatedto the extent that solids, biological matter and the like are filteredout in pretreatment steps that are well known in the art of wastetreatment (e.g. flocculation and settling tanks, biological treatmenttanks). The pretreatment steps are useful in removing materials thatwould have a tendency to clog, coat or otherwise interfere with theammonia recovery of the invention.

Referring now to FIG. 1, which is a simplified schematic of thereversible chemisorption apparatus and process 100. An aqueous stream101 containing ammonia contacts a sorbent stream 103 in anabsorber/reactor 105. Ammonia in the liquid is chemically bound to thesorbent (such as zinc oxide/zinc hydroxide) and the combined stream 107flows to a solid-liquid separator 109. The water stream 111 withsignificantly reduced ammonia concentration, can be reused ordischarged. A stream 113 containing the solid sorbent and ammoniacomplex can be heated in a heat exchanger 115 to thermally reverse thechemisorption as the heated stream 117. The heated stream 117 can beflashed in flash tank 119 to produce a concentrated vapor ammonia stream121 that may be used for chemical value or as a fertilizer. Theregenerated sorbent stream 123 may be recycled by means of a pump 125 orother conveyance. The recycle stream 127 may be cooled in a heatexchanger 129 before being returned to the absorber/reactor 105.

Referring to FIG. 2, which illustrates an alternate embodiment for theapparatus 200 and method of applying the reversible chemisorptionprocess. An aqueous stream 201 containing ammonia contacts a sorbent 203in a sorption column 205. The water stream 207, with significantlyreduced ammonia concentration, can be reused or discharged. Multiplesorption columns can be used in parallel or series. The sorption columnsmay be packed, fluidized, trayed, and the like. Chemical regeneration ofthe sorbent 203 may be achieved by periodically stripping the columnwith a weak nonchelating acid solution 211 such as formic, nitrous, oracetic acid. This removes the ammonia from the sorbent as an ammoniumsalt stream 213. Some applications may benefit from recycling the weakacid, which can be accomplished by adding an acid stream 215 (forexample, nitric acid or sulfuric acid) and distilling the mixture 217 ina distillation column 219. The resulting ammonium salt solution can bedischarged 221 while the recovered weak acid 223 can be condensed,cooled and recycled to the adsorption column during the nextregeneration/strip sequence.

Referring now to FIG. 3, there is shown a schematic diagram of onembodiment of the overall process using extraction with Zn(OH) and anitrogen reactor. Ammonia is not recovered in this process but isconverted to nitrogen. An ammonia containing liquid stream 301 from awater treatment plant obtained from the processing of a municipal sewageor an industrial effluent digested sludge is pumped with pump 303 into asettling tank 305. Excess settleable solids may collect in the bottomtank 305 and be sent back to the water treatment plant (not shown) bypump 307. The remaining liquid is pumped via pump 311 into mixer 313where it is mixed with a zinc and sodium hydroxide slurry from line 315.The ammonia in the liquid absorbs onto the zinc hydroxide. The materialsare sent to settling tank 323 via line 321. The combined ammonia/zinchydroxide materials precipitate and settle to the bottom of settlingtank 323. The sodium hydroxide is present in a concentration to adjustthe pH of the liquid to a preferred level of about pH 7 to 9. Zinchydroxide is only sparingly soluble at this pH and only an estimated 0.6ppm is lost to the deammoniated stream 325 that is returned to the watertreatment plant. The ion from the sodium hydroxide remains soluble andexits the process with stream 325. The ammoniated zinc hydroxide settlesto the bottom of tank 323 and thickens by gravitational forces. Thestream low in free ammonia exits the process via line 324.

The thickened—ammoniated zinc hydroxide flows from tank 323 and ispumped via pump 327 and lines 329 to decant centrifuge 331. The centratefrom the centrifuge 331 is recycled back to tank 323 via line 333. Thebulk of the ammoniated zinc hydroxide solids from centrifuge 331 arepressurized and heated via mixture with stream 335 in eductor 337 andthe mix is sent to mixer 339 via line 340. Fresh NaOH solution is addedin mixer 341 and blended from tank 343 vial pump 345 and lines 344. Thetemperature and pH of the stream in the output line 346 of mixer 341 aresufficiently high to cause substantially complete ammonia desorption andpartial dissolution of the zinc hydroxide. The ammonia-containing streamis sent to flash vessel 351 via line 346 where it is desorbed andflashed in vessel 351. The ammonia travels with steam from flash vessel351 via line 352 to absorber 353 where HNO₃ is added to form ammoniumnitrate (NH₄NO₃). The ammonia free-zinc and sodium hydroxide stream issent to pump 355 via line 354 and then to mixer 313 via line 315. Thepartially dissolved zinc hydroxide re-precipitates upon the pH change inmixer 313 and separator 323. The action of partially dissolving andre-precipitating the zinc hydroxide renews the crystal surfaces andmaintains the ammonia absorbing activity of the sorbent material. Thedistribution of the zinc hydroxide in soluble form also increases masstransfer kinetics for the absorption of ammonia in mixer 331 andsettling tank 323.

Nitric acid stored in tank 357 is pumped to absorber 353 via pump 359and lines 358 where formation of NH₄NO₃ takes place (it reacts with thefree ammonia to form an aqueous solution of concentrated ammonium). Thenitric acid is added to obtain a pH below 3 in the absorber 353 and toobtain an optimum molar ratio of nitric acid to ammonia of about 1.3 inthe following reactions in NitRem reactor 367. Ammonia vapor from line352 is immediately and quantitatively absorbed into the low pH solutionin absorber 353. The output of absorber 353 is pumped to tank 363 viapump 361 and lines 362. The NH₄NO₃ solution is stored in tank 363 andpumped to the NitRem reactor 367 by pump 365 and lines 364 for furtherreaction. Some cooling may be supplied at 363 or reactor 367 and/or line335 as needed to dissipate both the heats of reaction and the latentheat of condensation of both the ammonia and water. Since the stream inline 152 is a vapor above a high pH liquid, it contains substantially noHCl, no solids, and no mineral salts of any kind. At the worst it willcontain some hydrocarbon compounds and possibly some sulfur compounds.All of the materials that are volatile at the conditions in flash vessel351 are converted into very soluble non-odorous materials in ahydrothermal NitRem reaction in 367. Hydrocarbons are converted to waterand carbon dioxide, sulfur is converted to sulfuric acid, and thenitrogen compounds are converted to nitrogen gas.

The hydrothermal reactor system is described in the following U.S. Pat.Nos.: 5,221,486 and 5,433,868 to Fassbender. The reactor system consistsof only a pump, a high pressure reactor and controls. Due to the highconcentration of ammonium nitrate and the high exothermic reaction, noheat exchangers are required to maintain the reaction. Cold solutionfrom line 364 is pumped directly into the hot reactor 367 and the energyof reaction is sufficient to maintain the reactor 367 at hydrothermaltemperatures. Processed water and nitrogen gas are removed from thereactor 367 at full reactor temperature via line 368 and sent to apressure let-down system 369. The pressure is relieved to about 500 psi(350,000 kg/m²) where large quantities of nitrogen gas and steam areremoved. A portion of the high temperature liquid is used in stream 335to power eductor 337 and the excess gas and water may be returned to thewaste water treatment plant via line 371 or otherwise disposed of.

Efficiencies in the process are obtained by the following:

-   -   (1) the zinc regeneration step requires heat and the NitRem        reactor can supply that heat while simultaneously disposing of        the ammonia;    -   (2) the zinc regeneration step generates ammonia vapor, which        must be recovered in a condensed form. Nitric acid absorbs this        vapor with extremely high efficiency and generates a solution        optimal for processing with a NitRem reactor;    -   (3) the ammonium nitrate and nitric acid stream contains        substantially no mineral cations making processing in the        supercritical regime vastly simpler; the high concentration and        energy content of the ammonium nitrate stream allows for simple        reactor design and minimizes or eliminates the need for high        pressure heat exchangers; and    -   (4) the pH swing using sodium hydroxide renews the surface of        the zinc hydroxide crystals and enhances the kinetics and mass        transfer in absorbing ammonia.

EXAMPLE 1A

This example demonstrates that the ammonia adsorption is dependent bothupon the type of resin to which the ammonia binding metal is adsorbedand the process by which the metal is adsorbed to the resin. Four resinswere examined. Dowex™ 50WX2-400, Dowex™ 50WX2-100, and Dowex™ 50WX8-400are all strong acid ion exchange resins with a microporous styrene/DVBmatrix structure with sulfonic functional groups, produced by The DowChemical Company (Midland, Mich.). Dowex™ 50WX2-400 has 200-400 meshparticle sizes with 2% crosslinking. Dowex™ 50WX2-100 has 50-100 meshparticle sizes with 2% crosslinking. Dowex™ 50WX8-400 has 200-400 meshparticle sizes with 8% crosslinking. The Duolite™ ES-467 resin is aweakly acidic ion exchange resin with a macroporous polystyrene/DVBmatrix structure with amino-phosphonic functional groups and particlesizes of 16-50 mesh. Before loading with Zn, all four resins were washedthree or four times with deionized water.

In a first case, washed Dowex™ 50WX2-400 resin was subsequently loadedwith Zn by diluting 8 ml of resin to 50 ml using deionized water. Thisslurry was kept mixing throughout the rest of the loading procedureusing a small magnetic stir bar and a magnetic stirrer. A total of0.4269 g of ZnSO₄ was added to the slurry to provide Zn, along with0.300 ml of glacial acetic acid to provide buffering capacity betweenpH's 4 and 5. The pH of this solution was then adjusted to 1.2 using 850ml of 1 M H₂SO₄. The slurry was held at this pH for 15 minutes, beforeusing 8.7 ml of 1 M NaOH to raise the pH to between 4 and 5. The slurrywas held at this pH for two hours, before increasing the pH to 6.6 using3 ml of 1 M NaOH added in 0.5 ml increments. The resin removed from thestirred beaker and washed four times with deionized water beforediluting to 100 ml using deionized water for storage.

In a second case, washed Dowex™ 50WX2-400 resin was loaded with Zn bydiluting 8 ml of resin to 50 ml using deionized water. This slurry waskept mixing throughout the rest of the loading procedure using a smallmagnetic stir bar and a magnetic stirrer. A total of 0.2148 g of ZnO wasadded to the slurry to provide a source of Zn. The solution was then pHadjusted to 1.2 using 4.140 ml of 1 M HCl. The pH was held at 1.2 for 15minutes before gradually raising the pH to 7.1 by slowly adding 4.6 mlof 1 M NaOH. The resin was then washed four times with deionized waterbefore diluting to 100 ml using deionized water in preparation forstorage.

In a third case, washed Dowex™ 50WX2-100 resin was loaded with Zn bydiluting 16 ml of resin to 100 ml using deionized water. This slurry waskept mixing throughout the rest of the loading procedure using a smallmagnetic stir bar and a magnetic stirrer. A total of 0.4263 g of ZnSO₄was added to the slurry to provide a source of Zn along with 0.6 ml ofacetic acid to provide buffering capacity between pH 4 and 5. The pH ofthis slurry was then adjusted to 1.2 using 1.870 ml of 1 M H₂SO₄. The pHwas then held at 1.2 for 15 minutes before adjusting the pH to 4.2 using16.5 ml of 1 M NaOH. The slurry was then held between pH 4 and 5 for twohours before raising the pH to 6.7 using 7 ml of 1 M NaOH. The resin wasthen washed four times with deionized water before diluting to 100 mlusing deionized water in preparation for storage.

In a fourth case, washed Dowex™ 50WX8-400 resin was loaded with Zn bydiluting 16 ml of resin to 100 ml using deionized water. This slurry waskept mixing throughout the rest of the loading procedure using a smallmagnetic stir bar and a magnetic stirrer. A total of 1.2087 g of ZnSO₄was added to the slurry to provide a source of Zn along with 0.6 ml ofacetic acid to provide buffering capacity between pH 4 and 5. The pH ofthis slurry was not further adjusted since it had already been reducedto 1.0. During this time Zn²⁺ is loading and displacing H⁺ from RSO³H.The slurry was held at pH 1.0 for 15 minutes before adjusting it to 4.4using 34 ml of 1 M NaOH. The slurry was then held between pH 4 and 5 fortwo hours before raising the pH to 7.0 using 6.3 ml of 1 M NaOH. Theresin was then washed four times with deionized water before diluting to100 ml using deionized water in preparation for storage.

In a fifth case, washed Duolite ES-467 was loaded with Zn by diluting 25ml of resin to 200 ml using deionized water. This slurry was kept mixingthroughout the rest of the loading procedure using a small magnetic stirbar and a magnetic stirrer. A total of 2.8573 g of ZnSO₄ was added tothe slurry to provide a source of Zn along with 0.6 ml of acetic acid toprovide buffering capacity between pH 4 and 5. The pH of this slurry wasthen adjusted to 1.2 using 23 ml of 1 M H₂SO₄. The pH was then held at1.2 for 15 minutes before adjusting the pH to 4.4 using 45 ml of 1 MNaOH. After 45 minutes, the pH had dropped to 4.15 so an additional 3 mlof 1 M NaOH was added to raise the pH to 4.4. The slurry was then heldbetween pH 4 and 5 for an additional 1 hour and 15 minutes beforeraising the pH to 7.0 using 10.5 ml of 1 M NaOH. The resin was thenwashed three times with deionized water before diluting to 125 ml usingdeionized water in preparation for storage.

After loading each resin with Zn, the ammonia binding capacity of theresin at pH 8.0 was measured by diluting 3 ml of each resin to 85 mlusing deionized water. To this slurry 15 ml of 1000 ppm NH₃ solutionprepared from NH₄Cl was added to the slurry to bring the volume to 100ml. The slurry was then kept mixing using a magnetic stir bar and amagnetic stirrer while the pH was adjusted to 8.0 using 1 M NaOH. Thisrequired 62 and 70 μl of 1 M NaOH for the two trials using the resinprepared in Case 1; 150 and 146 μl of 1 M NaOH for the two trials usingthe resin prepared in Case 2; 30 and 20 μl of 1 M NaOH for the twotrials using the resin prepared in Case 3; 20 and 10 μl of 1 M NaOH forthe two trials using the resin prepared in Case 5; and 490 μl of 1 MNaOH for the trial using the resin prepared in Case 5. The slurries werekept mixing for 10 minutes, before centrifuging for 10 minutes to removethe resin from the supernatant. A total of 50 ml of supernatant was thencombined with 1 ml of 5 M NaOH to raise the pH above 12 convertingammonium ion to dissolved ammonia. Each supernatant's ammoniaconcentration was then measured using an Orion ammonia ion specificelectrode. The results are summarized in Table 1.

In a sixth case, the ammonia binding capacity of ZnO was measured byadding 0.2161 g of ZnO to 85 ml of deionized water. To this slurry 15 mlof 1000 ppm NH₃ solution prepared from NH₄Cl was added to the slurry tobring the volume to 100 ml. The slurry was then kept mixing using amagnetic stir bar and a magnetic stirrer while the pH was adjusted to8.0 using 1 M NaOH. This required 46 μl of 1 M NaOH. The slurry was keptmixing for 20 minutes, before centrifuging for 10 minutes to remove theZnO from the supernatant. A total of 50 ml of supernatant was thencombined with 1 ml of 5 M NaOH to raise the pH above 12 convertingammonium ion to dissolved ammonia. The supernatant's ammoniaconcentration was then measured using an Orion ammonia ion specificelectrode. The results are summarized in Table 1.

TABLE 1 Comparison of Ammonia Adsorption for Various Resins and ZincLoading Techniques ^(a,b) Loading Zinc Final NH₃ Fraction NH₃ ResinProcedure Source content (ppm) Adsorbed (%) Dowex ™ Case 1 ZnSO₄ 65.6 5650WX2-400 64.8 57 Dowex ™ Case 2 ZnO    89.0 41 50WX2-400 87.9 41Dowex ™ Case 3 ZnSO₄ 52.5 65 50WX2-100 54.3 64 Dowex ™ Case 4 ZnSO₄ 22.285 50WX8-400 22.6 85 Duolite ™ Case 5 ZnSO₄ 96.0 36 ES-467 None Case 6ZnO    151    0 ^(a) pH = 8.0 ^(b) initial NH₃ content was 150 ppm

A comparison of the results from Cases 1 and 2 show that the procedureused to load the Zn onto the resin can have a significant effect on thesubsequent ammonia adsorption properties of the resin. It is thoughtthat the chloride ion provided by the HCl used in Case 2 bound to the Znreducing the sites available for ammonia binding compared to that forthe identical resin in Case 1 prepared with H₂SO₄. The results indicatethat the type of zinc salt that is used to load the resin influences theresin's future ammonia adsorption capability and zinc salts with counterions with minimal affinities for zinc are preferred. A comparison of theresults for Cases 1 and 3 shows that varying the particle size of theresin also affects the ammonia binding capacity. Comparison of Cases 1and 4 shows that the crosslinking has a dramatic effect on the zincloaded resin's ammonia binding capacity. This is most likely due to theincreased amount of zinc, which the resin in Case 4 can bind compared toCase 1. The resin in Case 5 had a lower capacity for ammonia than eitherCase 1 or 4 even though its theoretical zinc binding capacity wassomewhere between that for those resins. It is thought that the zinc isbound much more tightly to amino phosphonate chelating the functionalgroups present in Case 5 than any of the other cases, reducing thezinc's capacity for ammonia binding by decreasing the potential for Znlosses from the resin. The results in Case 6 showed that unmodified ZnOhad no detectable activity as an ammonia sorbent.

Although the Zn was loaded to the resin in a batch slurry mode in allfive cases outlined here, it is not the only means of loading the Zn onthe resin. All that is required for metal loading on the resin is thecontacting of a solution of soluble metal salt with the resin in asolution with a high enough pH to avoid metal stripping from the resinby H⁺ or by supplying enough metal ions to outcompete the hydrogen ionsat the sorbent/resin loading site. This would include loading processessuch as passing ZnSO₄ or other soluble zinc salts across a packed bed ortower of the resin to be loaded. The preferred zinc salts are those thathave counter ions with a minimum of affinity for the zinc such as ZnSO₄.

EXAMPLE 2A

This example demonstrates that ammonia may be absorbed to a metalhydroxide adsorbent, and that the degree is dependent on the conditionsunder which the hydroxide is formed. Three different contacting schemeswere examined. In the first case, the insoluble Zn(OH)₂ precipitate wasformed in the presence of ammonia. In the second case, the insolubleZn(OH)₂ precipitate was formed in solution and then the ammonia wasadded to the solution. In the third case, the insoluble Zn(OH)₂precipitate was formed, recovered by filtration, washed, and then addedto an ammonia solution.

In a first case, 100 ml of 100 ppm NH₃ was prepared by adding 10 ml of1000 ppm NH₃ stock solution prepared from NH₄Cl to 90 ml of deionizedwater. This solution was kept mixing using a magnetic stir bar and amagnetic stirrer while 0.7990 g of ZnCl₂ was added. Upon the addition ofthe ZnCl₂, the slight formation of Zn(OH)₂ was observed. The pH of thesolution was then raised to 9.3 using 9.162 ml of 1 M NaOH. As the pHwas raised the amount of Zn(OH)₂ was visually observed to increase. OncepH 9.3 was reached, the solution was allowed to mix covered for 30minutes before the ammonia concentration was measured. The solution wasthen centrifuged for 10 minutes. 50 ml of the supernatant was combinedwith 1 ml of 5 M NaOH to raise the pH above 12 converting nearly all ofthe ammonium ion to ammonia, which was then measured using an Orionammonia ion specific electrode.

In a second case, 0.8063 g of ZnCl₂ was added to 90 ml of deionizedwater while stirring with a magnetic stir bar and a magnetic stirrer.Once again some slight precipitate formation was noted. The amount ofprecipitate was greatly increased when the pH was adjusted to 9.2 using8.532 ml of 1 M NaOH. To this slurry, 10 ml of 1000 ppm NH₃ stocksolution prepared from NH₄Cl was added. The solution's pH was thenadjusted to 9.3 using 0.345 ml of 1 M NaOH. The solution was held mixingfor 30 minutes before measuring the ammonia concentration. The slurrywas then centrifuged for 10 minutes. A total of 50 ml of the obtainedsupernatant was then combined with 1 ml of 5 M NaOH to raise the pHabove 12 converting nearly all of the ammonium ion to ammonia which wasthen measured using an Orion ammonia ion specific electrode.

In a third case, Zn(OH)₂ precipitate was prepared by dissolving 14.7 gof ZnCl₂ in 50 ml of deionized water and then adjusting the pH to 11.0using 5 M NaOH. This slurry was then filtered using a #2 Whatman filterin a Buchner funnel (tare wt.=233.0 g). The filter cake was then rinsedthree times using deionized water. The final weight of the Buchnerfunnel and the filter cake was found to be 256.6 g yielding 23.6 g ofZn(OH)₂ precipitate. 1.285 g of this precipitate was then added to 100ml of 100 ppm NH₃ solution prepared by adding 10 ml of 1000 ppm NH₃stock solution prepared from NH₄Cl to 90 ml of deionized water. Thisslurry was pH adjusted to pH 9.4 by adding 0.343 ml of 1 M NaOH and held15 minutes before measuring the ammonia concentration. The slurry wasthen centrifuged for 10 minutes. A total of 50 ml of the obtainedsupernatant was then combined with 1 ml of 5 M NaOH to raise the pHabove 12 converting nearly all of the ammonium ion to ammonia which wasthen measured using an Orion ammonia ion specific electrode.

The results from these three experiments are summarized in Table 2. Fromthis table it can be seen that the Zn(OH)₂ had the greatest capacity forammonia when it was formed in the presence of the ammonia as in Case 1.This capacity was somewhat reduced when the Zn(OH)₂ was prepared beforethe addition of the ammonia to the solution as in Case 2. Though theexact cause of this phenomenon is not known, it is suspected that thenumber of hydrated Zn groups on the particle surfaces directly exposedto the NH₃ is reduced in Case 2 compared to Case 1. The least ammoniaadsorption was observed in the case where the Zn(OH)2 was prepared,flitered and washed before addition to the ammonia solution as in Case3. Once again the exact cause of the loss of ammonia binding capacityhas not been determined though a number of hypotheses have been advancedincluding possible differences in precipitate surface area, particlesize, formation of a carbonate barrier layer, or the Zn(OH)₂ beingconverted to a different one of its six known morphological structures.

TABLE 2 Effect of Various Contacting Schemes on Ammonia Adsorption byZn(OH)₂ Contacting Fraction of Procedure Precipitate Formation NH₃adsorbed (%) Case 1 Formed in presence of NH₃. 12.3  Case 2 Formedbefore addition of NH₃. 9.6 Case 3 Formed, filtered, and washed before4.4 adding to NH₃ solution.

Although in each of these three cases, the Zn(OH)₂ was prepared fromZnCl₂ salt, this should not be taken as the only method available forforming the Zn(OH)₂ precipitate. All that is required for precipitateformation is the dissolution of a zinc salt in a concentration exceeding5×10⁻⁵ M followed by pH adjustment to a pH greater than 7 and less than13 with a preferred range of 9 to 11. In this laboratory Zn(OH)₂ hasalso been prepared using ZnSO₄ and soluble ZnCl₂ solutions prepared byreducing the pH of ZnO slurries to pH's of less than 2 using HCl. It isbelieved that as with the zinc loaded resins, different ammonia bindingcapacities will be observed for Zn(OH)₂ precipitates formed fromdifferent salts. The use of a batch contacting system to contact theprecipitate with the NH₃ should not be taken to exclude other contactingsystems including, but not limited to packed beds. All that is requiredfor adsorption is intimate contact between the precipitate and theammonia containing solution.

EXAMPLE 3A

In this example the dependence of the ammonia adsorption capacity ofzinc loaded resin as a function of the ammonia is demonstrated bypreparing an adsorption isotherm. The adsorption isotherm was determinedby combining a small amount of zinc loaded Dowex™ 50WX2-400 resin withvarying strength ammonia solutions at pH 8.0 and room temperature.

The Dowex™ 50WX2-400 resin was prepared by washing it three times withdeionized water. The Zn was loaded on the resin by diluting 20 ml ofwashed resin to 100 ml using deionized water and adding 0.3660 g of ZnO,while mixing using a magnetic stir bar and a magnetic stirrer. The pH ofthis solution was then reduced to less than 1.5 by adding 12 M HCl. Atthis pH, no insoluble ZnO was observed. The solution was held at this pHfor 30 minutes, before increasing the pH to greater than 7.0 using 0.1 MNaOH. The zinc loaded resin was then rinsed three times with deionizedwater. After washing the resin was diluted to a total volume of 100 mlfor storage.

The adsorption isotherm was generated by diluting three ml of zincloaded resin to 90 ml using deionized water. Varying amounts of 1000 ppmNH₃ stock solution prepared from NH₄Cl were then added to the slurry andthe pH was adjusted to 8.0 using 1 M NaOH. The solution was then mixedfor 15 minutes before centrifuging for 5 minutes. A total of 50 ml ofthe obtained supernatant was combined with 1 ml of 5 M NaOH to raise thepH to above 12 converting nearly all of the ammonium ion to ammoniawhich was then detected using an Orion ammonia ion specific electrode.The amounts of 1000 ppm NH₃ stock solution and 1 M NaOH added to eachsolution and the final NH₃ concentration achieved are summarized inTable 3.

TABLE 3 Results of Adsorption Isotherm Experiments. 1000 ppm NH₃ FinalNH₃ Stock Solution 1 M NaOH Total System Concentration Added (ml) Added(ml) Volume (ml) (ppm)  8 0.517  98.5 24.4 10 0.404 100.4 36.3 12 0.526102.5 44.9 14 0.691 104.7 53.7 18 0.707 108.7 73.0 25 0.803 115.8 113.9 

The total ammonia concentrations obtained above were converted todissolved NH₃ concentrations using a rearranged ammonia/ammoniumequilibrium expression:$\left\lbrack {NH}_{3} \right\rbrack = \frac{5.848 \times {10^{- 10}\left\lbrack {NH}_{3} \right\rbrack}_{T}}{10^{{- p}\quad H} + {5.848 \times 10^{- 10}}}$where [NH₃] is the concentration of dissolved ammonia at a given pH inmmoles/l and [NH₃]_(T) is the total combined ammonia/ammoniumconcentration in the solution in mmoles/l. These dissolved NH₃concentrations were plotted against the amount of ammonia absorbed pervolume of resin and fit with a Langmuir isotherm. The resulting Langmuirisotherm expression was:$Q = \frac{6.35\left\lbrack {NH}_{3} \right\rbrack}{\left( {0.218 + \left\lbrack {NH}_{3} \right\rbrack} \right)}$where Q is the specific ammonia adsorbance (grams of ammonia per literresin) and [NH₃] is the concentration of dissolved ammonia (mmoles/l).The Langmuir isotherm was fit to data as shown in FIG. 4. Thisexpression implies that the maximum achievable ammonia concentration onthis particular batch of resin is 6.35 NH3/l resin. This expression willvary depending on the metal loaded, resin used, past use, and loadingprocedure used among other factors. From this work it can be seen thatthe resin ammonia capacity will vary with the ammonia concentration inthe contacting waste stream. Although this isotherm was determined usinga batch contacting system, the results observed are not dependent uponthe contacting system used.

EXAMPLE 4A

In this example the dependence of the ammonia adsorption capacity ofZn(OH)₂ formed from ZnCl₂ precipitated in the presence of ammonia as afunction of the ammonia is demonstrated by preparing an adsorptionisotherm. The adsorption isotherm was determined by combining a smallamount ZnCl₂ with varying strength ammonia solutions at pH 9.5 and roomtemperature and adjusting the pH to 9.5 to form the Zn(OH)₂ precipitate.

Varying strength ammonia solutions were prepared by combining deionizedwater and 1000 ppm NH₃ stock solution prepared form NH₄Cl in varyingratios. To this solution 4 ml of 200 g/l ZnCl₂ solution was added. Thesolution was stirred until the ZnCl₂ crystals had dissolved, and thenthe pH was adjusted to 9.5 using 1 M NaOH. The slurries were keptstirring using a magnetic stir bar and magnetic stirrer for 30 minutes,before centrifuging to remove the Zn(OH)₂ precipitate. A total of 50 mlof supernatant were then combined with 1 ml of 5 M NaOH to raise the pHabove 12 before measuring the ammonia concentration using an Orionammonia ion selective electrode. The amount of deionized water, NaOH,and NH₃ stock solution used is summarized in Table 4.

TABLE 4 Results of Adsorption Isotherm Experiments using Zn(OH)₂. Total1 M NaOH 1000 ppm NH₃ Final [NH₃] Volume (ml) Added (ml) Added (ml)Total (ppm) 93.4 10.409  4 36.3 95.4 10.429  6 53.6 97.7 10.710  8 69  99.5 10.466 10 87.4 102.9  10.910 13 109.7  11.9 10.875 16 136   92.212.539 75 755  

The total ammonia concentrations obtained above were converted todissolved NH₃ concentrations using a rearranged ammonia/ammoniumequilibrium expression:$\left\lbrack {NH}_{3} \right\rbrack = \frac{5.848 \times {10^{- 10}\left\lbrack {NH}_{3} \right\rbrack}_{T}}{10^{{- p}\quad H} + {5.848 \times 10^{- 10}}}$where [NH₃] is the concentration of dissolved ammonia at a given pH inmmole/l and [NH₃]_(T) is the total combined ammonia/ammoniumconcentration in the solution in mmole/l. These dissolved NH₃concentrations were plotted against the amount of ammonia absorbed pervolume of resin and fit with a Langmuir isotherm a shown in FIG. 5. Theresulting Langmuir isotherm expression was: $\begin{matrix}{Q = \frac{0.143\left\lbrack {NH}_{3} \right\rbrack}{\left( {15.6 + \left\lbrack {NH}_{3} \right\rbrack} \right)}} & \quad\end{matrix}$where Q is the specific ammonia adsorbance (g NH₃/g Zn(OH)₂) and [NH₃]is the concentration of dissolved ammonia (mmole/l). This expressionimplies that the maximum achievable ammonia concentration on thisparticular batch of resin is 0.143 g NH₃/g Zn(OH)₂. This expression willvary depending on the particular metal hydroxide used, the salt fromwhich the hydroxide is prepared, past use, and particle size among otherfactors. From this work it can be seen that the resin ammonia capacitywill vary with the ammonia concentration in the contacting waste stream.Although this isotherm was determined using a batch contacting system,the results observed are not dependent upon the contacting system used.

EXAMPLE 5A

This example demonstrates the use of a weak organic acid to regenerate ametal loaded resin column after ammonia adsorption in a packed columnconfiguration. In this example, a Zn loaded Dowex™ 50WX2-400 resin waspacked into a 1 cm diameter column.

The Dowex™ 50WX2-400 ion exchange resin was washed three times withdeionized water and then 15.5 ml of washed resin were slurried indeionized water and combined with 0.4562 g of ZnO. The pH of thissolution was reduced to less than pH 1 using 5 M HCl at which all of theZnO was solubilized. The mixture was held at this pH for 5 minutes, thenraised slowly to pH 7.0 using 1 M NaOH. The resin was then washed withdeionized water and diluted to a total volume of 100 ml using deionizedwater. A total of 6.0 ml of the zinc-loaded resin was then packed into a1 cm diameter glass column by adding it in a deionized water slurry.

The column was loaded and regenerated using the following sequence.Deionized water was run through the column at 3 ml/min for five minutes.300 ml of 100 ppm NH₃ solution adjusted to pH 8.0 using 1 M NaOH waspassed through the column at 3 ml/min. 10 ml samples were collected.Deionized water was run through the column at 3 ml/min for five minutes.100 ml of 20 wt. % formic acid was run through the column at 3 ml/min toregenerate the resin. 4 ml samples were collected. Deionized water wasrun through the column at 3 ml/min for five minutes.

All of the samples were then analyzed for ammonia concentration byadding enough 5 M NaOH to raise the pH above 12 converting nearly all ofthe ammonium ion to ammonia which was measured using an Orion ammoniaion specific electrode. The results for three adsorption and desorptioncycles are presented in FIGS. 10 and 11. It can be seen from thesefigures that the formic acid was very effective at regenerating theresins' ammonia binding capacity. The increased ammonia binding seenafter regeneration may have been due to the removal of chloride ion fromthe resin bound Zn making more coordination sites available for ammoniabinding. It can also be seen from FIG. 10 that effluent ammoniaconcentrations of less than 5 ppm are readily and repeatably obtained.The use of the zinc metal ion, Dowex™ 50WX-2 ion exchange resin, andformic acid regenerant in an adsorption column should not be viewed asstating that other metals, resins, acid regeneration solutions andcontacting processes may not be used. All that is required to performammonia adsorption is the intimate contacting of the metal ion loadedresin or metal hydroxide with ammonia containing solutions. The resinmay then be regenerated, by providing intimate contact between anon-chelating weak acid and the ammonia containing resin in a batch orcontinuous mode.

In another alternative embodiment the aqueous slurry of the presentinvention is used for the treatment of a gas stream containing ammoniagas. For example, a gas stream from an acrylonitrile process would betreated by contacting with the aqueous slurry of the present inventionthat contains a slurry of metal hydroxide (e.g. ZnOH) or metal loadedmedia (e.g. Zn attached to polymeric beads). The contacting would be ina device known in the art such as a scrubber. When the aqueous slurrycontaining the extracted ammonia exits the scrubber it would be treatedto the recycle steps described herein.

In an alternative embodiment the regenerant weak acid (e.g. formic acid)can be regenerated using an electrochemical process that is well knownin the art.

The present invention can be used alone or in combination with othermethods such as air or steam stripping. In combination with othermethods for example, air stripping can be used to reduce the ammoniaconcentration to say 50 to 100 ppm at which time ligand exchangeadsorption would be used to reduce the concentration to low values suchas less than 10 ppm to less than 1 ppm. It can also be used to removeammonia from waste streams that can not be pH adjusted to a high pH,e.g. above a pH of 8 or 9.

Air stripping of a waste stream can be done using an air recycle stream,as exemplified by Saracco and Genon (1994). In this process, the pH ofthe waste stream is raised above 11 using lime to convert the ammonia toits gaseous form. The gaseous ammonia is then stripped from the wastestream using air. The ammonia is then removed from the air in theabsorption column using a sulfuric acid solution to convert the gaseousammonia to ammonium sulfate. The ammonium sulfate may then be disposedof, or recovered using a crystallize. The remaining ammonia remaining inthe waste stream is then recovered using the materials, methods, orapparatus of the herein disclosed invention.

Resins useful for preparation of sorbents of the invention may bemacroporous, a gel, hydrophilic, hydrophobic, or in the form of a solidporous sheet, hollow fiber membrane, or beads. Preferred resinstypically include both the acid form and the salt form (e.g. RSO₃H andRSO₃—Na⁺) and typically include resins from the examples below. Examplesof polymer backbones which are functional typically include for examplepolytrishydroxymethylacrylamide, polystyrene, polystyrene crosslinkedwith polystyrene divinyl benzene, and acrylic-divinyl benzene, agarose,cellulose, dextran, polymethacrylate, polystyrene-methacrylate orpolystyrene divinyl benzene-methacrylate. Specific examples of typicaluseful resins include:

-   -   Acrylamide type with a polytrishydroxymethylacrylamide polymer        backbone, such as the Trisacryl SP™ series resins that may be        obtained from Pharmacia Biotech Inc., Piscataway, N.J.    -   Amino phosphonate type with a polystyrene polymer backbone, such        as the Duolite™ ES 467 and C-467 resins that may be obtained        from Rohm and Haas Company.    -   Aminodiacetate type with a polystyrene or polystyrene divinyl        benzene polymer backbone, such as the Amberlite™ IRC 718 resins        that may be obtained from Rohm and Haas Company, Philadelphia,        Pa.    -   Carboxylate type with a acrylic-divinyl benzene, agarose,        cellulose, dextran, polymethacrylate, polystyrene-methacrylate        or polystyrene divinyl benzene-methacrylate polymer backbone,        such as the IONAC™ CC, SR-10, Z-5 and CCP™ series resins that        may be obtained from Sybron Chemicals, Birmingham, N.J.    -   Chelating tertiary amine type with a polystyrene divinyl benzene        polymer backbone, such as the Dowex™ XFS 4195, 4196, 43084        resins that may be obtained from Dow Chemical Co., Midland,        Mich.    -   Diphosphonate type with a polystyrene or polystyrene divinyl        benzene polymer backbone, such as the AGMP-50™ resins that may        be obtained from Bio-Rad Laboratories Inc., Richmond, Calif.    -   Diphosphonate, sulfonate type with a Styrene divinylbenzene        polymer backbone, such as the Ionac™ SR-12 resins that may be        obtained from Sybron Chemicals, Birmingham, N.J.    -   Phosphonate type with a cellulose or other polymer backbone,        such as the PM™ cellulose resins that may be obtained from        Pharmacia Biotech Inc., Piscataway, N.J.    -   Sulfonate type with an agarose, cellulose, dextran, polystyrene,        or polystyrene divinyl benzene polymer backbone, such as the        Dowex™ 50W, 50X, HCR and HGR series resins that may be obtained        from Dow Chemical Co., Midland, Mich.

The resins listed and described above are also typically used with thesecond general embodiment that is described in detail below.

The metal hydroxide used in the first general embodiment of theinvention may be macroporous, a gel, in the form of sheets, tubes,membranes, beads, and the like.

While zinc has been used throughout the examples for preparing metalhydroxides and for loading the metal loaded resins, other metals canalso be used. Metals useful include Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe(II and III), Hg, Mg, Mn, Ni, Pd, Zn, Zr and the like. The metals may beused alone or in combination with one or more other metals. These metalsare expected to have similar regeneration schemes as outlined above forzinc. Zinc is preferred because of its nontoxic character in relation toanimals and humans.

Weak acids useful in the invention, both for regenerating the metalhydroxides and the metal loaded resins, typically include those listedin Table 6. The weak acids useful in the invention generally have apK_(a) between about 3 to about 7.5 and preferably between 3 to 6.Another important requirement is that the acid be nonchelating or doesnot form chelating products during regeneration with respect to theloaded metal ion under the conditions of regeneration so as not to stripthe zinc metal from the resin. Both whey and AGS are useful in theinvention because they are cheap sources of the weak acids that theycontain.

Dimer, trimer, oligomeric, and polymeric nonchelating carboxylates arealso expected to be effective and especially provide low volatilityproperties for better ammonia and weak acid separation. For example,acrylic acid homopolymer, maleic anhydride homopolymer, ethylene/acrylicacid copolymer, ethylene/methylacrylic acid copolymer are useful in thisregard. The copolymer blend can be adjusted to minimize chelation by thepolycarboxylic acid. (Chelation can also be reduced by using propylenein place of ethylene.) Typically a chain length of up to about 100repeat units is preferred in order to obtain a water miscible carboxylicacid. Most preferred are oligomers having up to about 10 repeatingunits.

Water immiscible carboxylic acids are also expected to be useful withthe invention. When water immiscible carboxylic acids are used, themetal containing sorbent must first be washed with an intermediatepolarity solvent to remove water from the sorbent to prevent thecarboxylic acid from precipitating on the sorbent, or by preventingaccess to the ammonia by poor wetting of the resin by the carboxylicacid, and thereby reducing or preventing its ability to strip ammoniafrom the resin. An example of such an intermediate solvent is an alcohol(e.g. methyl, ethyl, isopropyl, or butyl alcohol), or ketones (e.g.acetone, methyl ethyl ketone, etc.), etc. A water solubility of only afew percent is required for the solvent to be effective in removingwater from the resin prior to elution of the ammonia by the carboxylicacid. Other appropriate solvents are known to those skilled in the art.

After washing the resin with the alcohol, a non-chelating waterimmiscible carboxylic acid stripping solution is contacted with theresin to remove ammonia from the sorbent. Thereafter, before reuse as asorbent, the sorbent is again washed with alcohol or other appropriatesolvent to remove any remaining stripping solution. The alcohol or otherappropriate solvent is recovered by distillation after it has becomesufficiently loaded with immiscible carboxylic acid, where upon thecarboxylic acid is also recycled back to the stripping operation, or theammonia recovery operation, part of the process. The ammonia loadedstripping solution is separated from the sorbent and can be treated todrive off the ammonia. One method of removing and recovering the ammoniais by heating, optionally with a vacuum to augment the process.Preferably the carboxylic acid is sufficiently high boiling that theammonia is recovered. Distillation can also be used to recover anyalcohol, or other wash solvent, and to remove entrained water, althoughthese steps may not be critical other than to maintain fluid balance ofalcohol, water, and water immiscible carboxylic acid volumes in thecircuit.

A second means of recovering the ammonia from the water immisciblecarboxylic acid (ammonium carboxylate) phase is to wash the phase withan aqueous solution, such as aqueous sulfuric acid or aqueous nitricacid, whereupon the water immiscible carboxylic acid phase isregenerated and recycled. The ammonia then in the form of an ammoniumsulfate or ammonium nitrate solution respectively which can be isolatedas product or sent to Nitrem(TM) processing to dinitrogen as alreadydescribed. By using concentrated aqueous acid strip solutions,concentrated ammonium salt solutions can be produced making them ofvalue for ammonia recovery and/or reducing the size and cost ofprocessing equipment used for recovery or processing of the ammoniaproduct.

Ammonia can also be released from the water immiscible carboxylic acidby treatment with alkaline material in solid or solution form using forexample packed columns or stirred tanks. For example, caustic soda, sodaash, magnesium hydroxide, or lime could be used to provide thisalkalinity. In such cases the freed neutral ammonia gas would berecovered, and the carboxylate salt regenerated by treatment with acidgenerating a waste salt solution or gypsum slurry.

A third means for recovering the ammonia from said water immisciblestrip solution is to wash it with aqueous metal salt solution containingexcess acid. For example the zinc sulfate/sulfuric acid solutionpreviously described provide such a solution. The resultant ammonicalsolution then can be processed to a double salt as before.

Typically, the immiscible carboxylic acid should be branched and haveeight or more carbon atoms (including the branches) so that it is a highboiling fluid, for example alpha-C12 alkyl succinates, versatic acids,neodecanoic acid, 2-ethylhexanoic acid, etc. Straight chain carboxylicacids of eight or more carbon atoms are also useful if dissolved in anappropriate water immiscible solvent with an appropriately high boilingpoint, for example methyl isobutyl ketone, kerosenes of high flash point(e.g. Norpar 13, Isopar M, Alkylate 6, etc.), or alcohols (e.g.isodecanol). Also, non-water soluble carboxylic acid polymers andoligomers as described above for the water soluble versions can also beused as an ammonia stripping material if a solvent or co-solvent is usedto keep the ammonia stripping material in solution.

The spent weak acid containing the ammonia (e.g. ammonium carboxylate)can also be regenerated from its ammonium salt by reaction with nitrousacid follows:RCOO⁻NH₄ ⁺+HNO₂→RCOOH+N₂+2H₂O(spent sorbent solution) (recycled to sorbent regeneration)Such nitrous acid can be derived from several sources separately or incombination, for example a mixture of sodium nitrate and strong mineralacid, or with a mixture of nitric acid and easily reducible substancesuch as waste organic material (food waste, biomass solids from wastebiotreatment, low grade syrups, sugars, carbohydrates, organics alreadypresent in the waste from which the ammonia was sorbed and followed theammonia by sorption on the bed, etc.). Such conditions are well known inthe art as “Bouveault Amide Hydrolysis” conditions (p.86 of “Guide toOrganic Reactions” by Howard D. Weiss, Burgess Publ. Co., Minneapolis,Minn., 1969).

The above reactions avoid the expensive distillation step to recover theweak acid. The conditions are milder than those of the NitRem processdescribed herein. Under some conditions there still may be a need tocontrol water balance by distillation of a purge stream. The weak acidshould be selected to be resistant to oxidative attack by nitrous acid.For example acetic acid, propionic acid, adipic acid, succinic acid, theAGS mixture, etc. (Table of weak acids) should all be effective. Weakacids with alpha-hydroxy groups, e.g. glycolic acid, would not beeffective since it would also be easily oxidized by the nitrous acid.

TABLE 6 Typical Examples of Acceptable Regenerant Weak Acids COMPOUNDpKa Acetic acid 4.8 Adipic acid 4.4 Anilinium ion 4.6 Benzoic acid 4.2n-butyric acid 4.8 Fumaric acid 3.0 Formic acid 3.7 Sulfoanilium ion˜4     Maleic acid 6.2 o-phthalic acid ˜3     Propionic acid 4.9Succinic acid 4.2 Tartaric acid 3.0 Lactic acid 3.9 Carbonic acid 6.4Cyanic acid 3.7 Ferrocyanic acid 3.0 Hydrofluoric acid 3.0 Nitrous acid3.3 Glycolic acid 3.0 Hydroxylammonium ion 6.0 Whey (source of lacticacid) 3.8 AGS¹ ˜4.2   Hydrogen phosphate monobasic ion 7.2 ¹A = adipicacid, G = glutaric acid, S = succinic acid, AGS is an adipic acidmanufacturing byproduct of a mixture of these dicarboxylic acidsTables 7 and 8 list typical examples of acids that are unacceptablebecause of chelation or because of ionization where the pK_(a) is toolow.

TABLE 7 Typical Examples of Unacceptable Regenerant Acids Due toChelation COMPOUND pKa Citric acid 3.1 EDTA salt 6.2 Glycine 2.4 NTA 3.9Malonic acid 2.9 Oxalic acid, monoprotic salt 4.3 Pyrophosphoric acid,monobasic 2.4 1,10-Phenanthrolinium 5.0

TABLE 8 Typical Examples of Unacceptable Regenerant Acids Due low pKaExamples of Unacceptable Regenerant Acids Due low pKa Arsenic acid 2.3Phosphoric acid 2.2 Hydrogen sulfate 2.0 (2^(nd) proton on the sulfate)Sulfurous acid 1.8 Sulfuric acid >1     Nitric acid >1     Hydrochloricacid >1     Hydrobromic acid >1     Methane sulfonic acid >1    Trifluroacetic acid >1    

Although zinc has been used throughout the examples for producing thesorbents such as the ion exchange resin and the metal hydroxide, othermetals can also be used. Metals useful for producing the sorbentsinclude Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd and the like. These metals areexpected to have similar regeneration schemes as outlined above forzinc. Zinc is preferred because of its nontoxic character in relation toanimals and humans.

The preferred loading pHs for several metals disclosed herein are:silver (Ag) below 8, cadmium (Cd) below 6.7, chromium (Cr) below 5.2,cobalt (Co) below 6.8, copper (Cu) below 5.2, mercury (Hg) below 1.8,nickel (Ni) below 6.7, and zinc (Zn) below 6.8. As is known to thoseskilled in the art the upper limit is primarily determined by the pH atwhich a metal hydroxide precipitate forms. It should be noted that inpreparing the resins of the examples that the first holding step at alow pH of about 1.2 is optional.

While not wishing to be bound by any particular hypothesis or theory,the theoretical explanations provided below are offered to help guide aperson skilled in the art in understanding and using the invention. Thefollowing “chemistry model” as it is presently understood is useful foroptimizing the performance or guide the selection of sorbent and NH₃complexing metal ion materials to match a particular metal loadedsorbent system to a particular feed stream containing ammonium ion orammonia. The findings from the examples herein are:

Stripping the ammonia from the sorbent with a strong acid alone elutessome of the NH₃-absorbing metal ion from the resin along with most ofthe ammonium ion despite the much higher charge of the metal ionrelative to hydrogen ion (normally 2+ vs. 1+).

-   -   High concentrations of monovalent cations elute some of the NH₃        absorbing metal ion on the resin along with the ammonium ion        despite its much higher charge (2+ vs. 1+).    -   Non-chelating weak acids are effective sorbent regenerants as        they remove the ammonia, but not significant quantities of the        NH₃ complexing metal ion, and the preferred use of non-chelating        weak acids that also do not strongly sorb onto the sorbent,        leaving residual acidity there which interferes with the NH₃        sorption cycle.    -   Complexing anions can affect the NH3 absorbing behavior of the        sorbent.

Operational chemistry models are put forth below to aid in sorbentsystem selection for each of the above four findings.

Monovalent Ion Effects

For a monovalent cation, such as Na⁺, to displace a +2 charged NH₃complexing metal ion from the sorbent, either the Na⁺ concentrationneeds to be very high, or the sorbent donor groups are too separated forcooperative bonding with the divalent metal ion, or a combination ofthese. The crosslinked, sulfonated polystyrene resins are largely usedfor water softening which requires easy removal of divalent hardnessmetal ions (Ca²⁺, Mg²⁺, Fe²⁺) using a NaCl brine regenerant solution.

It is believed that on the average, these water softening resins havewidely spaced —SO₃ ⁻ groups, such that the NH₃ complexing metal ion,e.g. Zn²⁺, can only bond to one —SO₃ ⁻ group at a time, thus requiringthe presence of another anion (e.g. OH⁻, Cl⁻, SO₄ ⁼, OAc⁻, etc.) forcharge balance. Therefore, the +2 metal ion behaves as an easily eluted+1 metal ion illustrated as follows:R—SO₃ ⁻(ZnX)⁺where ZnX⁺ can be (ZnCl)⁺, (Zn²⁺ (SO₄ ⁼)_(1/2)), (ZnOAc)⁺, etc.

This mode of ion sorption is sufficient in the water softening casewhere the cations in the feed water are dilute and the competition forthem minimal. However it is expected that NH₄ ⁺ contaminated waters maycontain significant concentrations of other cations, such as Na⁺, and itis desired that the NH₄ ⁺ be removed selectively over these othercations to avoid having to regenerate the sorbent too often. These otherions are normally dischargeable in the waste stream and their recoveryis not wanted. Therefore, the above chemistry model indicates thepreferred sorbent for the NH₃ complexing metal ion in the case wheremonovalent ions are present is one where the —SO₃ ⁻ groups are in closeproximity to one another, for example vicinal or gem, for exampleRCH(SO₃ ⁻)₂ (e.g. Sybron IONAC SR-12) or chelation (e.g. amino methylenephosphonate, R—NHCH₂PO₃H⁻, as is presented in the Serolite®ES-467). Itwill be useful in preparing the metal ion loaded feedstock of suchsorbents that the NH3-complexing metal ion be added at one half of theamount of binding sites present to facilitate bonding of two resinbinding sites per metal ion. In addition, if the acid form of the resinis used, that this excess acidity is neutralized, using NaOH forexample, but that pHs greater than that needed for metal hydroxideprecipitation be avoided until after any excess metal ion is removed bywashing. It is believed that excess metal ion left on the resin may formmetal hydroxide precipitate solids which could block microchannels inthe sorbent, thereby reducing the apparent ammonia loading capacity. Itis also wasteful of ammonia binding metal. Lastly, for ion exchangeresins (non-chelating) there is also a probability that only one ionicbond to the metal ion will form, thereby resulting in the metals beingheld less tightly resulting in a portion of the metal ions being lostduring use. These effects of the excess metal are less desirable than astoichiometrically matched sorbent preparation but are still acceptableas the sorbent will be cycled many times during which the optimumcomposition naturally forms with the associated enhancement inperformance (FIG. 8).

Effectiveness of Non-chelating Weak Acids, Especially Those of LowHydrophobicity

Removal of the NH₃ from the NH₃ ⁻ loaded sorbent with minimal loss ofNH₃ binding metal ion requires a balance of properties. The prior art,which used mineral acids to elute ammonium ion without the use of metalsalts, also shows unacceptable losses of metal ion sorbent. It has nowbeen discovered that acids can be used to elute ammonia as NH₄ ⁺provided the pK_(a) of the acid is in the range of 3 to 7.5, preferably3-6, and is none chelating. The following is the presently understoodchemical explanation for this capability. Ion exchange resins, forexample the sulfonated resin described elsewhere, function by exchangingone metal cation with another, either more highly charged or at higherconcentration, or both, at the site of the anionic RSO₃ ⁻ group(s). Itis believed that strong acids (pKa <3, especially <1) have high ionicconcentrations of H⁺ and its counter ion. In using columns or other“multi-staging” contactor, this effect becomes very pronounced as theNH₃-binding metal ion is forced by ion exchange to gradually (or rapidlyat desirably high mineral acid concentrations) move down the column,leading to a steady bleeding of the NH₃-binding metal ion from thesorbent bed. The use of dilute acid eluants is undesirable since itleads to dilute NH₄ ⁺ product eluant. Also, because of the above platetheory, and the requirements on toxic metal discharges, even dilutesolutions of mineral acids lead to unacceptable losses of theNH₃-binding metal. However, weak acids possess similar amounts ofacidity as mineral acids with which sorbed NH₃ can be converted to NH₄⁺, but <1 percent of the hydrogen ion is present in ionized form. Infact, it is possible to have >99.999 percent of the acidic hydrogenpresent as the neutral molecule. For example, dissolved in water aceticacid is as CH₃COOH and not CH₃COO⁻+H⁺, formic acid is as HCOOH and notHCOO⁻+H⁺, while sulfuric acid, a strong mineral acid, is 100 percent asdissociated H⁺+HSO₄ ⁻.

A second requirement is that the weak acid not be chelating in the pHregion where the NH₃ is being eluted as NH₄ ⁺. Chelation of theNH₃-binding metal by anionic, deprotonated weak acids, e.g. citric acid[HOOCCH₂CH(OH)(COOH)CH₂COOH] would leach the NH₃-binding metal from thesorbent. Tables 6 and 7 serve as a guide to selecting suitable weakacids with which to practice the invention.

Competitive Effects of Metal Ion Complexing Anions

The unique selectivity of the invention is believed to be due in part tothe formation of a chemical bond between the NH₃-binding metal ion ofthe sorbent and the nitrogen atom of the NH₃ molecule. This chemistryprovides selectivity for ammonia over the bulk of the cations, anions,and neutral molecules also contained in the water with theammonia/ammonium ion. This understanding explains why in certaininstances certain anions and neutral molecules appear to compete withammonia for the sorption sites, thereby lowering the apparent capacityfor ammonia. For example, chloride ion forms metallo-chloro bonds withsome metals, e.g. Zn²⁺, but not with others, e.g. Ni²⁺. Therefore, ifsignificant chloride ion levels are expected in the ammonia contaminatedfluid, then an ammonia-binding metal such as Ni²⁺ should be selected.This effect can be used to advantage by co-sorbing more than one solutefrom a feed solution. All that is required is that a sufficient quantityof sorbent is provided to provide the capacity to handle all of thecontaminants expected including the ammonia. Examples of othercontaminants which could be removed along with the ammonia are organicamines, cyanide ion, hydrogen cyanide, halides, etc.

II. Second General Embodiment

Broadly, the invention includes methods, materials, and apparatus forremoving ammonia from fluid streams. The fluid streams include gaseousand liquid streams. When gaseous streams are used the ammonia from thegaseous stream is first extracted into a liquid stream and thenextracted from the liquid stream.

Two main embodiments for ammonia recovery are disclosed herein. Thefirst uses zinc sulfate for directly contacting a fluid stream and thesecond uses a metal-loaded ion exchange medium for contacting the fluidstream. Both embodiments are able to reversibly bind ammonia in adecomposable salt so that overall costs for the methods are reduced.Specifically, both embodiments use contact of ammonia (or ammonium) withzinc sulfate and sulfuric acid to produce a solution of mixed sulfatesand then concentrate the solution sufficiently to cause crystallizationof an ammonium zinc sulfate hydrate double salt. The crystals may thenbe heated in a known manner to release NH₃ and regenerate the zincsulfate and sulfuric acid. As used herein the following terms havemeanings as follows:

-   -   Sorbent—as used herein includes polymeric materials and solid        materials having a surface area able to bind ammonia. The term        sorbent and its related terms of speech are used generally        herein to include both chemical and physical absorbents and        adsorbents.    -   Metal-loaded media—as used herein includes metal loaded ion        exchange materials, chelating materials, zeolites, and organic        or inorganic materials. The important characteristic for these        metal loaded media is that they be capable of reversibly binding        ammonia. The metal should be firmly bound to the substrate        material so as not to substantially unbind during the conditions        of use. The metal loaded media should bind ammonia on exposure        to an ammonia containing fluid stream and give up the ammonia        when exposed to a strong acid.    -   Hydrate—as used herein means the hydrated form of the compound        with any degree of hydration. For the ammonium zinc sulfate        hydrate, the hexahydrate is the preferred compound and the most        likely crystallization product according to the invention.

Pretreatment of the waste streams used in the invention is contemplatedto the extent that solids, biological matter and the like are filteredout in pretreatment steps that are well known in the art of wastetreatment (e.g. flocculation and settling tanks, biological treatmenttanks). The pretreatment steps are useful in removing materials thatwould have a tendency to clog, coat or otherwise interfere with theammonia recovery of the invention.

The invention stems from the recognition that when ammonium sulfate andzinc sulfate are present in a solution at concentrations exceeding thesolubility limit, they may combine to form crystals of a hydrated zincammonium sulfate, probably (NH4)₂SO₄.ZnSO₄.6H₂O (zinc ammonium sulfatehexahydrate). These crystals are monoclinic and described as white ortransparent (CRC Handbook of Chemistry and Physics 63rd edition, andMellor's A Comprehensive Treatise on Inorganic and TheoreticalChemistry, 1929). Mellor notes that with an excess of ammonium sulfate,a near quantitative crystallization of the Zn is possible. Thecrystallization may be described by the expression:2NH₄ ⁺+Zn²⁺+2SO₄ ²⁻+6H₂O⇄(NH₄)₂SO₄ZnSO₄.6H₂O.The water solubility of this compound is given in the CRC Handbook as 7g/100 g water at 0° C. and 42 g/100 g at 80° C. The solubility for theammonia or zinc sulfates may be shifted by adding an excess of the othercomponent. The CRC Handbook also notes that the compound decomposesbefore reaching its melting point.

The present invention comprises the use of ammonium zinc sulfate hydrateto selectively recover ammonia from an aqueous solution in a solidcrystalline form. The water and ammonia may then be recovered by heatingthe crystals and recovering the water and ammonia in the off gases. Thisprocess would then leave behind zinc sulfate and sulfuric acid, whichcan be resolubilized and recycled.

While not being bound by any hypothesis or theory, the chemical reactionmodels provided below are offered to help guide the skilled person inthe art in using the invention and in understanding possibleexplanations of the reactions. They may or may not accurately describethe exact conditions, which may prevail while practicing the invention.

The decomposition of the crystals may be described as:

 (NH₄)₂SO₄.ZnSO₄.6H₂O_((s))+heat→2NH_(3(g))+Zn(HSO₄)_(2(s,l))+6H₂O_((g))

The heating may occur at a single temperature releasing both the waterand the ammonia together, or at two or more separate temperatures. Thefirst is a lower temperature process in which the crystals are brokendown into water, zinc sulfate, and ammonium sulfate as shown by:(NH₄)₂SO₄.ZnSO₄.6H₂O_((s))+heat→(NH₄)₂Zn(SO₄)_(2(s,l))+6H₂O_((g))If the temperature is then increased, the zinc sulfate will melt, andthe ammonium sulfate will decompose as follows:(NH₄)₂Zn(SO₄)_(2(s,l))+heat→2NH_(3(g))+Zn(HSO₄)_(2(s,l))This decomposition is expected to initially occur between 200 and 250°C. It is also possible that under more severe temperature conditions thesulfuric acid may be evaporated to a significant extent or even brokeninto sulfur dioxide and water. This may be avoided to a great extent bykeeping the temperature below about 330° C. If further heat treatmentoccurs, this may lead to the decomposition of the zinc bisulfate as:Zn(HSO₄)_(2(s,l))+heat→ZnSO_(4(s,l))+H₂O_((g))+SO_(3(g)).

A schematic of the one embodiment of the invention utilizing ZnSO₄directly to reduce ammonia from aqueous solution using thecrystallization scheme is shown in FIG. 14. An aqueous ammonia stream401 enters an evaporator 402 along with a zinc sulfate and sulfuric acidsolution 409. Preferably the acid is in excess, so that the pH is lessthan neutral, preferably less than about 4.

The two solutions react in the evaporator 402 to produce a solution ofzinc sulfate and ammonium sulfate. The evaporator then concentrates thestream (if necessary) by removing water 410 by conventional heating,vacuum or a combination of the two. The amount of evaporation requireddepends upon the initial concentration of the ammonia. If the ammoniaconcentration is high enough (resulting in ammonium sulfateconcentration above the solubility limit) no evaporation may be requiredto reach the solubility limit of the zinc ammonium sulfate hydrate. Itis apparent to those skilled in the art that a combination of theconcentration, temperature and pressure can be used to controlcrystallization.

The resulting concentrated solution 403 is sent to the crystallizer 404.The crystallizer may be viewed as any single piece or combination ofpieces of equipment capable of cooling the solution below thecrystallization temperature and continuously or sequentially separatingthe crystals of zinc ammonium sulfate hydrate 406 from the mother liquor405. Depending on the level of contaminants in the ammonia stream 401,multiple crystallization steps may be necessary. Zinc may also berecovered from the liquor 405 from the crystallizer 404 using a cationexchange resin or liquid-liquid extraction and with sulfuric acidregeneration. Optionally, the liquor 405 may be recycled and mixed withthe ammonia stream 401 and/or the zinc sulfate/sulfuric acid solution409. Again, a separate crystallizer may not be necessary if theconcentration is raised sufficiently in the evaporator to precipitatethe crystals in that equipment. Or the two steps (concentration andcooling) could be done in one vessel.

The amounts of ammonium sulfate and zinc sulfate exiting with the liquor405 will depend on a number of controllable factors, including, but notlimited to, the ratio of zinc sulfate to ammonium sulfate, absoluteconcentrations obtained in the evaporator, and the temperature at whichcrystallization is performed. The concentration of zinc or ammonia inthe liquor 405 exiting the crystallizer may be reduced virtually to zeroby operating in great excess of the other component.

The zinc ammonium sulfate hydrate crystals 406 are decomposed, forexample, in oven 407 to release NH₃ and H₂O in stream 408 while the zincsulfate and sulfuric acid 409 are recycled. The oven 407 may actually betwo or more ovens operating at multiple temperatures or one oven mayoperate stepwise at increasing temperature to sequentially remove thegases. Operating at low temperatures may remove most of the water, whileoperating at temperatures exceeding about 200° C. may then be used torecover the ammonia. The gaseous ammonia stream may be condensed torecover the ammonia or recovered as a salt by stripping the stream withan acid.

Under certain conditions, SO₃ may also be released while decomposing thecrystals. This is not generally desired, but may occur under aggressivedecomposition. In this case, it may be possible to capture the SO₃ andNH₃ downstream in a scrubber as ammonium sulfate.

The formation and decomposition of ammonium zinc sulfate hydratecrystals may also be used to reduce the ammonia concentration of streamscontaining high levels of ammonia by direct treatment. The economics ofthis process are obviously improved by the fact that the need forevaporation is reduced. FIG. 15 shows a schematic of this process in thecase where ammonia is in excess. In this case the wastewater stream 501containing high levels of ammonia is concentrated in the evaporator 502with the removal of water 510 and sent to the crystallizer 504. Theresulting solution is cooled below the crystallization temperature toproduce the crystals of zinc ammonium sulfate hydrate 506, which aresent to the oven 507. The remaining aqueous stream 505 leaving thecrystallizer 504 will still contain ammonia, but this can be furtherreduced if necessary through the addition of adsorption columns. Onceagain, the zinc ammonium sulfate hydrate crystals are decomposed in oven507 to release NH₃ and H₂O in stream 508 while the zinc sulfate andsulfuric acid 509 are recycled.

Another preferred method to reduce the ammonia concentration of aqueousstreams is the use of ligand exchange adsorption using zinc adsorbed toa cation exchange resin and then regenerating the resin using aZnSO₄/H₂SO₄ solution. This has proven to be very effective at removingthe ammonia from the resin, surprisingly, without detrimental strippingof the zinc off the cation exchange resin. To be economically viable,the ZnSO₄ and the ammonia in the regeneration solution must beseparated, so that the ZnSO₄ may be reused. FIG. 16 is a schematicdrawing of apparatus for the formation and decomposition of ammoniumzinc sulfate hydrate crystals which may be used to perform thisseparation when the ammonia is present in excess.

In the loading step, the ammonia-laden wastewater stream 601 contactsand is adsorbed by a sorbent (such as a zinc-loaded cation exchangeresin) in an adsorption column 602. The discharged water stream 603,with significantly reduced ammonia concentration, can be reused ordischarged. Multiple sorption columns can be used in parallel or series.The sorption columns may be packed, fluidized, trayed, and the like.

In the second step, chemical regeneration of the sorbent may be achievedby periodically stripping the column with the ZnSO₄ and H₂SO₄ stream612. This strips the ammonia from the sorbent and carries it as anammonium sulfate/zinc sulfate spent regeneration solution stream 604 tothe evaporator 606 where the solution is concentrated by removal ofwater 605.

It has been discovered that the high acid stripping does not result inthe detrimental removal of zinc from the resin (or from the column).While zinc may be continuously stripped to some degree during theregeneration step, the presence of Zn in the stripping solution causeswhat seems to be an equilibrium between the zinc ion in the aqueousphase and the bound form on the resin. So even if it is continuouslystripped, it is also continuously replenished in the steady state.

Evaporation may be carried out in the conventional manner by, forexample heating, vacuum or a combination of the two. The amount ofevaporation required depends upon the initial concentration of theammonia. If the ammonia concentration is high enough no evaporation maybe required to reach the solubility limit of the ammonium zinc sulfatehydrate. It is apparent to those skilled in the art that a combinationof the concentration, temperature and pressure can be used to controlcrystallization by reducing the solution to conditions below thesolubility limit of zinc ammonium sulfate hydrate.

The resulting concentrated stream from the evaporator 606 is thendischarged to the crystallizer 607 where the temperature is reducedbelow the crystallization temperature of the zinc ammonium sulfatehydrate. Again, a separate crystallizer may not be necessary if theconcentration is raised sufficiently in the evaporator to precipitatethe crystals in that equipment. The resulting crystals 609 are separatedand discharged to the oven for regeneration of the zinc sulfate andsulfuric acid as described above. The remaining crystallizer aqueousstream 608 may be further processed to recover the ammonium sulfate,which can be sold or converted to sulfuric acid and ammonia throughheating. The water and ammonia vapor stream 611 from the decompositionin the oven 610 may actually be two streams, one from a lowertemperature oven containing the majority of the water and a second froma higher temperature oven containing the majority of the ammonia. Theammonia may be captured as ammonia by condensation or as a salt by usingan acid stripper. The regenerated zinc sulfate and sulfuric acid arerecycled to the sorption column 602. Makeup water 613 (preferablycondensed from stream 605) may be added back to the stripping solutionbefore return to the column.

FIG. 17 is a schematic drawing of apparatus and process for ammoniarecovery from waste streams by use of ammonium zinc sulfate hydratecrystallization and decomposition in the regeneration of zinc-loaded ionexchange resin where zinc is in excess. The process is similar to thatshown in FIG. 16 except that the crystallizer aqueous stream 708contains largely ZnSO₄ which may be directly recycled back asregeneration solution, and substantially all of the ammonia exits fromthe ovens 710 in stream 711. The apparatus and streams have thefollowing identifiers:

Wastewater stream containing ammonia—701 Sorption column—702 Treatedwastewater—703 Zinc Sulfate/Ammonium Sulfate solution—704 Evaporatedwater—705 Evaporator—706 Crystallizer—707 ZnSO₄ liquid streamcontaining—708 Zinc ammonium sulfate hydrate crystals—709 Oven—710 NH₃,H₂O offgas—711 ZnSO₄/H₂SO₄ recycle stream—712 Water makeup—713

EXAMPLE 1B

A 0.25 M ZnSO₄ solution containing 15,000 ppm of NH₃ in the form ofammonium sulfate was prepared. A total of 200.3 g of this solution wasplaced in a 250 ml flask, left open to the air, and boiled on a hotplateuntil the mass of the solution was reduced to 57.2 g. The solution wasthen left to cool on the counter until the formation of crystals wasfirst noted. The flask was then placed in an ice bath to form additionalcrystals. The crystals were translucent white in color. The crystalswere collected using a Buchner funnel. A total of 24.2 g of crystals wasrecovered. A fraction containing 9.718 g of the crystals was added to analuminum weigh pan and placed in a drying oven at approximately 150° C.for approximately 2 hours. Visual examination of the solids after dryingshowed that they had become an opaque white powder losing much of theircrystalline appearance. When the solids were reweighed, they were foundto have been reduced to 6.965 g. This weight loss would be consistentwith the loss of the water from the hydrated ammonium zinc sulfate.

The ammonia concentration of the crystals and the white powder wasmeasured, by redissolving a measured quantity of the crystals or powderin a known amount of water, which was subsequently measured for ammoniaconcentration using an ammonia Orion ion specific electrode. Thecrystals were found to be 7.4% ammonia, while the dried powder was foundto be 11.8% ammonia by weight. When the weight difference is taken intoaccount, it can be seen that this initial drying did not remove anysignificant quantities of ammonia. Subsequently, 0.8601 g of the driedpowder was placed in an aluminum weigh pan and gently heated with apropane torch. Melting was observed in the powder along with theevolution of a white gas. The torch heated powder was reweighed andfound to have a mass of 0.7263 g. The powder was then resolubilized andmeasured for ammonia. The torch dried powder was found to have anammonia concentration of 8.07% by weight corresponding with an ammoniareduction of 33.8% relative to the undried crystals.

The use of a furnace to remove the ammonia from the oven dried crystalswas also performed. A 1.0437 g sample of the oven dried powder wasplaced in an aluminum weighed pan, then heated to 300° C. for 2 hours.When the sample was reweighed, it was found to have been reduced to0.935 g. The powder was found to have an ammonia concentration of 8.2%by weight corresponding to an ammonia reduction of 29.7% relative to theundried. The use of the furnace was then repeated on 1.0092 g of ovendried powder at 350° C. for 2 hours. The weight of this sample wasreduced to 0.7048 g and the powder was found to have an ammoniaconcentration of 5.0% by weight, corresponding to an ammonia reductionof 66.2% relative to the undried crystals. The results of theseexperiments are summarized in Table 1.

TABLE 1 Results Summary Sample Relative Relative Ammonia Ammonia ContentMass (g sample/g Content (g ammonia/g Sample undried crystals) (wt %)undried crystals) Undried Crystals 1.000 7.4 0.074 Oven dried powder0.717 11.8  0.085 150° C. Torch treated 0.605 8.1 0.049 powder Furnacetreated 0.638 8.2 0.052 powder 300° C. Furnace treated 0.501 5.0 0.025powder 350° C.

EXAMPLE 2B

A second trial was made in an attempt to repeat the crystallizationresults observed in Example 1B and to determine the amount of ammonialost during boiling. A fraction of the recovered crystals from Example1B was weighed, placed in a drying oven at approximately 150° C. for 2.5hours, and reweighed. A visual inspection of the dried powder showedthat it had become more opaque and lost much of its original crystallineappearance. A 35.6% weight loss was found during drying which would beconsistent with the removal of the hydration water and some free waterfrom the crystals. As in Example 1B, samples of the dried powder and theundried crystals were solubilized and measured for ammoniaconcentration. The undried crystals were found to have an ammoniaconcentration of 7.52% and the dried powder was found to have an ammoniaconcentration of 11.80%. When corrected for the weight loss, this resultindicates that no ammonia was lost during this low temperature drying.This is consistent with the hypothesis that the ammonium zinc sulfatehydrate can be dried at relatively low temperatures to remove thehydration water. Samples of the oven-dried powder were then placed in afurnace at 300° C. and 350° C. for 2 hours. The samples showedrespective weight losses of 7.5% and 37.4% relative to the dried powder.The ammonia concentrations in the furnace treated powders were 8.6% and3.1% for the powders treated at 300° C. and 350° C. respectively. Theresults from the second trial are summarized in Table 2.

TABLE 2 Results Summary Sample Relative Relative Ammonia Ammonia ContentMass (g sample/g Content (g ammonia/g Sample undried crystals) (wt %)undried crystals) Undried Crystals 1.000 7.5 0.075 Oven dried powder0.644 11.8  0.076 150° C. Furnace treated 0.596 8.6 0.051 powder 300° C.Furnace treated 0.403 3.1 0.012 powder 350° C.

EXAMPLE 3B

A total of 200 ml of a 0.25 M ZnSO₄ solution containing 14,286 ppmammonia in an ammonium sulfate form was prepared and placed in apreweighed 250 ml flask with a magnetic stir bar. The pH of thissolution was adjusted to 5.5 using 1 M NaOH. A 10 ml sample of thissolution was taken before the flask was corked and attached to a gasdispersion tube containing 400 ml of 0.1 M H₂SO₄. The flask was thenplaced on a hot plate and boiled until the mass of the solution wasreduced from 201 g to 66.9 g. The flask was then disconnected from thegas dispersion tube and allowed to cool in the ambient air until thefirst crystals began to form. The flask was then placed in an ice bathfor further crystal formation. The cooled solution was then filteredusing a Buchner funnel to recover the crystals. A total of 20.7 g ofcrystals was recovered along with 42.8 g of spent mother liquor. Thecontents of the gas dispersion tube were also collected and were foundto weigh 575.7 g. A fraction of the collected crystals was then placedin a drying oven at approximately 150° C. for 2.5 hours. Samples of theresultant dried powder were further heat treated by placing them in afurnace at 304° C. for two hours or 309° C. for six hours or 350° C. for2 hours. The ammonia concentrations of the crystals and heat treatedpowders were then measured by dissolving them in a known quantity ofwater and measuring the ammonia concentration with an ammonia ionselective electrode. The results of this experiment are presented inTable 3.

TABLE 3 Summary of Results from Heat Treatment of Crystals % Ammonia %Mass Sample Treatment Removed Removed Undried Crystals 0.0 0.0 CrystalsDried at 150° C., −1.0 35.6 2.5 hr. Powder Heat Treated at 32.7 42.3304° C., 2 hr. Powder Heat Treated at 74.5 53.9 309° C., 6 hr. PowderHeat Treated at 84.0 59.7 350° C., 2 hr.

EXAMPLE 4B

This example demonstrates that a ZnSO₄/H₂SO₄ solution may be used tostrip ammonia from a zinc loaded ion exchange resin. A small laboratoryadsorption column was set up containing 6 ml of Dowex 50WX8-400 ionexchange resin preloaded with Zn²⁺. This was loaded with ammonia bypassing approximately 45 bed volumes of dilute ammonium sulfate solutionwith an ammonia concentration of 1000 ppm and a pH of 8.0 over thecolumn. The column was then rinsed with deionized water before passingapproximately 13 bed volumes of 0.5 M ZnSO₄ solution, which had been pHadjusted to 4.0 using 1 M H₂SO₄. A fraction collector was used tocollect approximately 6.5 ml samples of the spent regeneration solution.These samples were pH adjusted to greater than pH 12.0 using 5 M NaOHand the ammonia concentration was measured using an ammonia ionselective electrode calibrated against 0.5 M ZnSO₄ solution with a knownammonia concentration. The concentration profile clearly showed theexistence of stripped ammonia in the spent regeneration solution.

EXAMPLE 5B

This example demonstrates that a ZnSO₄/H₂SO₄ solution may be used toload metal ions on a column and to regenerate a column, which has beenloaded with ammonia. A small laboratory adsorption column was filledwith 6 ml of Dowex 50WX8-400 ion exchange resin. The resin bed waswashed by flowing deionized water through the column at 3 ml/min for 45minutes. The column was then loaded with Zn²⁺ ions by running an aqueoussolution containing 0.5 M ZnSO₄/5% H₂SO₄ through the column at 3 ml/minfor 45 minutes. The column was then rinsed using deionized water at 3ml/min for 45 minutes.

This column was used to remove ammonia from a municipal wastewatercentrate sample obtained from the Jackson Pike Municipal Wastewatertreatment facility in Columbus, Ohio. This sample was centrifuged andfiltered through a What an #40 paper filter to remove large particulatematter. The pH of the sample was found to be 8.35 and the ammoniaconcentration of the sample was found to be 1140 ppm. The filtered,wastewater centrate was fed to the column at 3 ml/mm and 20 samplescontaining 160 seconds off effluent were collected. The ammonia was thestripped from the column using an aqueous solution containing 0.5 MZnSO₄/5% H₂SO₄ that was fed to the column at 2 ml/mm for 50 minutes. Thecolumn was finally rinsed with deionized water at a flowrate of 3 ml/mmfor 30 minutes. The collected samples ammonia concentration was measuredby adjusting the pH to greater than 12 with sulfuric acid and measuringthe ammonia concentration using an Orion ion specific electrode. Thetotal ammonia adsorbed on the column was determined by differences. Theammonia loading/stripping procedure was then repeated on the same columnin an identical manner.

In the first run, a total ammonia loading of 16.3 g NH₃/l of resin wasachieved. Following the regeneration of the resin using 0.5 M ZnSO₄/5%H₂SO₄ a total ammonia loading of 15.9 g NH₃/l of resin was achieved. Anapproximately 97% recovery of the Zn²⁺ loaded resins was obtainedfollowing regeneration. This demonstrates the effectiveness of 0.5 MZnSO₄/5% H₂SO₄ for loading and regenerating the resin.

Resins useful with the second general embodiment are the same as thoselisted in the first general embodiment above.

While zinc has been used throughout the examples for preparing metalsulfates (or other salts) and for loading the metal loaded resins, othermetals can also be used. Metals useful include Ag, Cd, Co, Ca, Cr, Hg,Mg, Mn, Zn, Zr, Fe (II and III), Ce, Cu, Al, Ni, Pd, and the like. Themetals may be used alone or in combination with one or more othermetals. These metals are expected to have similar regeneration schemesas outlined above for zinc. Zinc is preferred because of its nontoxiccharacter in relation to animals and humans and its solubilityproperties as a salt and double salt.

While sulfuric acid has been used throughout the examples for reactingwith the ammonium to form the ammonium salt, other strong acids such assulfurous, phosphoric, carbonic or hydrochloric may be used. Obviously,they may have some properties that may reduce their value in someapplications, but they may find some use.

The preferred loading pHs for several metals disclosed herein are:chromium (Cr) below 5.2, cobalt (Co) below 6.8, copper (Cu) below 5.2,nickel (Ni) below 6.7, and zinc (Zn) below 6.8. As is known to thoseskilled in the art the upper limit is primarily determined by the pH atwhich a metal hydroxide precipitate forms. It should be noted that inpreparing the resins of the examples that the first holding step at alow pH of about 1.2 is optional.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all of the possible equivalent forms or ramificationsof the invention. It is to be understood that the terms used herein aremerely descriptive, rather than limiting, and that various changes maybe made without departing from the spirit of the scope of the invention.

1. A method for removing ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent and produce an ammonia depleted fluid; b. separating said ammonia depleted fluid from said ammonia loaded sorbent; c. separating said ammonia from said ammonia loaded sorbent by contacting said sorbent with a regenerant stripping solution comprising (1) a non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, wherein an ammonium salt solution is formed producing a spent stripping solution and regenerated sorbent; or (2) a strong acid and a metal salt, wherein an ammonium salt solution is formed producing a spent stripping solution and regenerated sorbent; and d. separating said spent stripping solution from said regenerated sorbent.
 2. The method according to claim 1, wherein said sorbent comprises sorbent types selected from the group consisting or polymers of acrylamides containing metal complex groups, of aminophosphonates, aminodiacetates, carboxylates, phosphonates, diphosphonates, and sulfonates including chelators.
 3. The method according to claim 1, comprising separating ammonia from said spent stripping solution.
 4. The method according to claim 1, wherein a metal cation loaded on said metal cation loaded media is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 5. A method for recovering ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent; b. separating said ammonia loaded sorbent from said fluid; c. separating said ammonia from said ammonia loaded sorbent by contacting said sorbent with a stripping solution comprising (1) a non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, wherein said sorbent is regenerated and an ammonium-weak acid salt solution is formed in a spent stripping solution; or (2) sulfuric acid and zinc sulfate salt, wherein said sorbent is regenerated and an ammonium-zinc sulfate hydrate solution is formed in a spent stripping solution; d. separating said spent stripping solution from said regenerated sorbent; e. separating said ammonium-weak acid salt or said ammonium-strong acid salt from said spent stripping solution; and f. treating said ammonium salt solution to recover products therefrom.
 6. A method for recovering ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent and produce an ammonia depleted fluid; b. separating said ammonia depleted fluid from said ammonia loaded sorbent; c. separating said ammonia from said ammonia loaded sorbent by contacting said ammonia loaded sorbent with a regenerant comprising a non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, wherein an ammonium regenerant salt solution is formed.
 7. The method according to claim 6, comprising: separating at least some of said ammonium from said ammonium regenerant salt.
 8. The method according to claim 7, comprising: separating said ammonium from said ammonium regenerant salt with a step selected from the group consisting of: heating, applying a vacuum, and a combination thereof.
 9. The method according to claim 6 comprising: separating said ammonium from said regenerant salt by the step of contacting with a strong acid to form regenerant and an ammonium strong acid salt; and separating said regenerant therefrom.
 10. The method according to claim 6 comprising: wherein said regenerant is a weak organic acid.
 11. The method according to claim 6 comprising: contacting and reacting said separated ammonia with nitric acid to form ammonium nitrate; and heating said ammonium nitrate and reacting at a temperature and pressure under hydrothermal conditions to decompose said ammonium nitrate to substantially nitrogen gas and water.
 12. An apparatus for recovering ammonia from a fluid comprising: means for enclosing a metal cation loaded media able to reversibly load ammonia; inlet means, at an inlet portion of said means for enclosing, for admitting fluid or regenerant; outlet means, at an outlet portion of said means for enclosing, for exiting treated fluid or reacted regenerant; and regenerant source means comprising non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, operatively connected to said inlet means.
 13. A method for recovering ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising a metal cation loaded media, in a manner adapted to load ammonia on said sorbent; b. separating said ammoniated sorbent and said fluid; c. separating said ammonia from said ammoniated sorbent by contacting said ammoniated sorbent with a non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates to form a regenerant/ammonia salt; and d. separating said ammonia from said regenerant by one or more steps selected from the group consisting of: (1) heating said ammonia/regenerant complex; (2) applying a vacuum to said ammonia/regenerant complex; and (3) contacting said ammonia/regenerant complex with a strong acid.
 14. The method according to claim 13, comprising: e. recycling said sorbent and/or said regenerant.
 15. The method according to claim 13, comprising: wherein said regenerant comprises a weak organic acid.
 16. An apparatus for recovering ammonia from a fluid comprising: a. a container enclosing a metal cation loaded media, said metal loaded media able to reversibly load ammonia; b. an inlet in said container for admitting fluid or regenerant to said container; c. an outlet in said container for exiting treated fluid or reacted regenerant from said container; and d. a source of regenerant comprising non-chelating weak acid having a pK_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, operatively connected to an inlet at said container.
 17. The apparatus according to claim 16, comprising: e. an ammonia separator for receiving and separating ammonia from said regenerant, operatively connected to said outlet.
 18. The apparatus according to claim 17, comprising: a chemical reactor operatively connected to said ammonia separator, for reacting separated ammonia from said separator with a strong acid; and a regenerant separator, operatively connected to said reactor, for separating said regenerant from said strong acid.
 19. The apparatus of claim 18, comprising recycling apparatus for providing regenerant from said regenerant separator to said inlet.
 20. The apparatus of claim 17, comprising: f. a reactor for mixing and reacting nitric acid, operatively connected to said ammonia separator, for producing ammonium nitrate; and g. a hydrothermal reactor, operatively connected to said reactor, for degrading said ammonium nitrate to nitrogen gas and water.
 21. The apparatus according to claim 16, wherein a metal cation loaded on said metal cation loaded media is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 22. A method for removing ammonia from a fluid comprising: a. contacting said fluid with a sorbent of metal cation loaded media in a manner adapted to load ammonia onto said sorbent; b. separating said fluid from said ammonia-loaded sorbent; c. contacting said separated ammonia loaded sorbent with a stripping solution of a strong acid and a metal salt, wherein an ammonium salt is formed with said metal salt in a spent stripping solution and said ammonia loaded sorbent is regenerated to a sorbent of metal cation loaded media; d. separating said spent stripping solution from said regenerated sorbent of metal loaded media; and e. treating said separated spent stripping solution in a manner adapted to crystallize an ammonium-metal therefrom.
 23. The method according to claim 22, comprising crystallizing said ammonium salt by increasing the concentration of said ammonium salt and metal salt in said spent stripping solution by evaporation, by decreasing the temperature of highly concentrated solutions, or by a combination of evaporation and decreasing temperature.
 24. The method according to claim 23, wherein said crystallization conditions comprise seeding with recycled ammonium sulfate crystals to minimize scaling and to control crystallization rate and crystal size.
 25. The method according to claim 23, wherein a metal cation loaded on said metal-loaded media is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 26. The method according to claim 22, comprising using metal cation loaded media wherein a metal cation loaded on said metal cation loaded media is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 27. The method according to claim 26, comprising metal cation loaded media wherein said metal cations may be used alone or in combination with one or more other metal cations.
 28. The method according to claim 26, comprising using a metal salt wherein a metal salt of said stripping solution is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 29. The method according to claim 28, comprising using metal cations alone or in combination with one or more other metal cations.
 30. The method according to claim 22, wherein the metal cations of said metal cation loaded media and the metal salts of said stripping solution are derived from the same metal.
 31. The method according to claim 22, wherein the metal cations of said metal cation loaded media and the metal salts of said stripping solution are derived from zinc.
 32. The method according to claim 22, wherein the metal cations of the metal cation loaded media and the metal salts of said stripping solution are derived from metals that form double salts with ammonia.
 33. The method according to claim 22, wherein said strong acid in said stripping solution is selected from the group consisting of sulfuric, sulfurous, phosphoric and hydrochloric.
 34. The method according to claim 22, wherein said strong acid is sulfuric acid.
 35. The method according to claim 22, comprising the additional steps of separating at least some of the ammonia from the salt and recycling at least some of the remaining constituents for preparation of said stripping solution.
 36. The method according to claim 35, comprising the additional step of separating said ammonia from said ammonium-metal double salt by decomposition with heat.
 37. The method according to claim 22, wherein the sorbent types useful in the invention are selected from the group consisting of polymers of acrylamides containing metal complex groups, of aminophosphonates, aminodiacetates, carboxylates, phosphonates, diphosphonates, and sulfonates including chelators made therefrom, and mixtures of the foregoing.
 38. A method for removing ammonia from wastewater comprising: a. contacting an ammonia-laden wastewater stream with a zinc-loaded cation exchange resin to load the ammonia; b. separating said zinc-loaded cation exchange resin containing said loaded ammonia and stripping the ammonia with a stripping solution of ZnSO₄ and H₂SO₄ to form a spent regeneration solution of ammonium sulfate and zinc sulfate; and c. crystallizing zinc ammonium sulfate hydrate therefrom.
 39. The method according to claim 38, comprising the additional step of recovering said zinc ammonium sulfate hydrate and decomposing to recover ammonia.
 40. The method according to claim 39, comprising the step recovering zinc sulfate and sulfuric acid from said decomposition recycling.
 41. The method according to claim 39, comprising crystallization of the zinc ammonium sulfate hydrate by evaporation of the spent regeneration solution by heating, vacuum, or a combination of heating and vacuum, and subsequent cooling.
 42. The method according to claim 41, wherein after crystallization of said spent regeneration solution, the remaining aqueous liquid is further processed to recover ammonium sulfate or is recycled back for use in preparing stripping solution.
 43. The method according to claim 39, wherein said crystals are decomposed by heating, wherein water and ammonia vapors are released.
 44. The method according to claim 43, wherein the crystals are heated at a first lower temperature to remove water, and subsequently heating at a second higher temperature to remove ammonia.
 45. The method according to claim 44, wherein said heating reaction is continued to release SO₂/SO₃ gas; and then capturing said gas as ammonium sulfate in an absorption column.
 46. The method according to claim 45, wherein said ammonia is captured as ammonia by condensation or as a salt by using an acid stripper.
 47. The method according to claim 45, wherein said acid stripper is phosphoric or nitric acid.
 48. An apparatus for recovering ammonia from an ammonia-containing fluid comprising: a. a fluid-contacting device containing an ammonia sorbent of metal cation loaded media; b. means for contacting said ammonia-containing fluid with said ammonia sorbent and loading said ammonia thereon to form an ammonia-depleted fluid; c. means for removing said ammonia-depleted fluid from the contacting device; d. means for contacting said ammonia-loaded sorbent with a stripping solution of a strong acid and a metal salt to form a spent regeneration solution of ammonium salt and metal salt wherein said strong acid and said metal salt are present in said means for contacting said ammonia loaded sorbent; and e. means for treating said spent regeneration solution to crystallize an ammonium-metal double salt therefrom.
 49. The apparatus according to claim 48, further comprising: f. an evaporator for increasing the concentration of said ammonium salt and metal salt in said spent regeneration solution and/or a cooling device for cooling said spent regeneration to cause crystallization.
 50. The apparatus according to claim 49, wherein said evaporator and said cooling device comprise the same piece of apparatus.
 51. The apparatus according to claim 50, further comprising a condenser to recover said ammonia vapor or a contacting device to capture ammonia as a salt by using an acid stripper.
 52. The apparatus according to claim 48, further comprising one or more heating devices for decomposing said crystals to release water and ammonia vapors.
 53. The apparatus according to claim 48, wherein a metal cation loaded on said metal cation loaded media is derived from a metal selected from the group consisting of Ag, Cd, Co, Cr, Cu, Hg, Ni, Pd, Zn, and combinations thereof.
 54. A method for recovering ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent and produce an ammonia depleted fluid; b. separating said ammonia depleted fluid from said ammonia loaded sorbent; c. washing said ammonia loaded sorbent with an intermediate polarity solution to remove water therefrom; d. separating said ammonia from said ammonia loaded sorbent by contacting said ammonia loaded sorbent with a stripping solution of a regenerant comprising a substantially water insoluble non-chelating weak carboxylic acid having a pK_(a) of 3 to 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, wherein regenerated sorbent and an ammonium regenerant salt solution is formed in a spent stripping solution; e. separating said spent stripping solution from said regenerated sorbent; and f. washing said regenerated sorbent with an intermediate polarity solvent to remove residual carboxylic acid therefrom before reuse thereof.
 55. The method according to claim 54, comprising: g. separating said ammonium salt solution from said spent stripping solution.
 56. The method according to claim 55, wherein ammonia is recovered from said salt by heating.
 57. The method according to claim 55, wherein ammonia is recovered from its ammonium weak acid salt solution by reaction with nitric acid or nitrous acid under mild conditions of heat at less than 100C.
 58. The method according to claim 57, wherein said weak acid salt is derived from an acid selected from the group consisting of acetic acid, propionic acid, adipic, acid, succinic acid, and AGS.
 59. The method according to claim 54, wherein said carboxylic acids are selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric nonchelating carboxylates.
 60. The method according to claim 59, wherein said carboxylates are acrylic acid homopolymer, maleic anhydride homopolymer, ethylene/acrylic acid copolymer, or ethylene/methylacrylic acid copolymer.
 61. The method according to claim 59, wherein said carboxylates have a chain length of up to about 100 repeat units.
 62. The method according to claim 59, wherein said carboxylates are oligomers having up to about 10 repeating units.
 63. An apparatus for recovering ammonia from a fluid without detrimental stripping of metal from an exchange resin comprising: means for enclosing a metal cation loaded exchange resin able to reversibly load ammonia; inlet means, at an inlet portion of said means for enclosing, for admitting fluid or regenerant; outlet means, at an outlet portion of said means for enclosing, for exiting treated fluid or reacted regenerant; and regenerant source means comprising non-chelating weak acid having a pK_(a) of 3 to 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, operatively connected to said inlet means.
 64. A method for removing ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent and produce an ammonia depleted fluid; b. separating said ammonia depleted fluid from said ammonia loaded sorbent; c. separating said ammonia from said ammonia loaded sorbent by contacting said sorbent with a regenerant stripping solution comprising a strong acid and a metal salt, wherein an ammonium salt solution is formed producing a spent stripping solution and regenerated sorbent; and d. separating said spent stripping solution from said regenerated sorbent.
 65. A method for removing ammonia from a fluid comprising: a. contacting said fluid with a sorbent comprising metal cation loaded media at conditions adapted to load ammonia onto said sorbent and produce an ammonia depleted fluid; b. separating said ammonia depleted fluid from said ammonia loaded sorbent; c. separating said ammonia from said ammonia loaded sorbent by contacting said sorbent with a regenerant stripping solution comprising a non-chelating weak acid having a pk_(a) of about 3 to about 7.5, and which is selected from the group consisting of dimeric, trimeric, oligomeric, and polymeric carboxylates, wherein an ammonium salt solution is formed producing a spent stripping solution and regenerated sorbent; and d. separating said spent stripping solution from said regenerated sorbent. 